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THE

ADVANCE OF SCIENCE

IX THE

LAST HALF-CENTURY

BY

T. H. HUXLEY, P.B.S.

?0£hj.

'1-

NEW YORK
D. APPLETON AND COMPANY

1887

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10.5
H r l8

Reprinted from " The Reign of Queen Vic-
toria, a Survey of Fifty Years of Progress,"
edited by Thomas Humphrey Wood, M. A.,
London,

THE ADVANCE OF SCIENCE
IN THE LAST HALF-CENTURY

The most obvious and the most dis- Recent

. . indus-

tinctive features of the History of Civili- trial
sation, during the last fifty years, is the progrc '
wonderful increase of industrial produc-
tion by the application of machinery, the
improvement of old technical processes
and the invention of new ones, accompa-
nied by an even more remarkable devel-
opment of old and new means of locomo-
tion and intercommunication. By this
rapid and vast multiplication of the com-
modities and conveniences of existence,
the general standard of comfort has been
raised ; the ravages of pestilence and fam-
ine have been checked; and the natural
obstacles, which time and space offer to

4 THE ADVANCE OF SCIENCE

mutual intercourse, have been reduced in
a manner, and to an extent, unknown to
former ages. The diminution or removal
of local ignorance and prejudice, the
creation of common interests among the
most widely separated peoples, and the
strengthening of the forces of the organi-
sation of the commonwealth against those
of political or social anarchy, thus ef-
fected, have exerted an influence on the
present and future fortunes of mankind
the full significance of which may be di-
vined, but cannot, as yet, be estimated at
its full value,
caused This revolution — for it is nothing less

by the . . n . . _ .. '

increase- — in the political and social aspects of
LJscf modern civilisation has been preceded,
accompanied, and in great measure
caused, by a less obvious, but no less
marvellous, increase of natural knowl-
edge, and especially of that part of it
which is known as Physical Science, in
consequence of the application of scien-

ence.

IN THE LAST HALF-CENTURY.

tific method to the investigation of the
phenomena of the material world. Not
that the growth of physical science is an
exclusive prerogative of the Victorian
age. Its present strength and volume
merely indicate the highest level of a
stream which took its rise, alongside of
the primal founts of Philosophy, Litera-
ture, and Art, in ancient Greece ; and,
after being dammed up for a thousand
years, once more began to flow three cent-
uries ago.

It may be doubted if even-handed Greek

and me-

justice, as free from fulsome panegyric as aiaeval

science

from captious depreciation, has ever yet
been dealt out to the sages of antiquity
who, for eight centuries, from the time
of Thales to that of Galen, toiled at the
foundations of physical science. But,
without entering into the discussion of
that large question, it is certain that the
labors of these early workers in the field
of natural knowledge were brought to a

6 THE ADVANCE OF SCIENCE

standstill by the decay and disruption of
the Roman Empire, the consequent dis-
organisation of society, and the diversion
of men's thoughts from sublunary matters
to the problems of the supernatural world
suggested by Christian dogma in the Mid-
dle Ages. And, notwithstanding sporadic
attempts to recall men to the investiga-
tion of nature, here and there, it was not
until the fifteenth and sixteenth centuries
that physical science made a new start,
founding itself, at first, altogether upon
that which had been done by the Greeks.
Indeed, it must be admitted that the men
of the Renaissance, though standing on
the shoulders of the old philosophers,
were a long time before they saw as much
as their forerunners had done.

The first serious attempts to carry
further the unfinished work of Archi-
medes, Hipparchus, and Ptolemy, of
Aristotle and of Galen, naturally enough
arose among the astronomers and the

IN THE LAST HALF- CENTURY. 7

physicians. For the imperious necessity
of seeking some remedy for the physical
ills of life had insured the preservation of
more or less of the wisdom of Hippocrates
and his successors ; and, by a happy con-
junction of circumstances, the Jewish and
the Arabian physicians and philosophers
escaped many of the influences which, at
that time, blighted natural knowledge in
the Christian world. On the other hand,
the superstitious hopes and fears which
afforded countenance to astrology and to
alchemy also sheltered astronomy and the
germs of chemistry. Whether for this,
or for some better reason, the founders of
the schools of the Middle Ages included
astronomy, along with geometry, arith-
metic, and music, as one of the four
branches of advanced education; and, in
this respect, it is only just to them to ob-
serve that they were far in advance of
those who sit in their seats. The school-
men considered no one to be properly

Renais-
sance.

8 THE ADVANCE OF SCIENCE

educated unless he were acquainted with,
at any rate, one branch of physical sci-
ence. We have not, even yet, reached
that stage of enlightenment.
Further Iii the early decades of the seven-
after teenth century, the men of the Renais-
sance could show that they had already
put out to good interest the treasure be-
queathed to them by the Greeks. They
had produced the astronomical system
of Copernicus, with Kepler's great addi-
tions ; the astronomical discoveries and
the physical investigations of Galileo ;
the mechanics of Stevinus and the 'De
Magnete ' of Gilbert ; the anatomy of the
great French and Italian schools and the
physiology of Harvey. In Italy, which
had succeeded Greece in the hegemony
of the scientific world, the Accademia dei
Lyncei and sundry other such associa-
tions for the investigation of nature, the
models of all subsequent academies and
scientific societies, had been founded ;

IN THE LAST HALF-CENTUKY. 9

while the literary skill and biting wit of
Galileo had made the great scientific ques-
tions of the day not only intelligible, but
attractive, to the general public.

In our own country, Francis Bacon Francis

d Bacon.

had essayed to sum up the past 01 physi-
cal science, and to indicate the path which
it must follow if its great destinies were
to be fulfilled. And though the attempt
was just such a magnificent failure as
might have been expected from a man of
great endowments, who was so singularly
devoid of scientific insight that he could
not understand the value of the work al-
ready achieved by the true instaurators of
physical science ; yet the majestic elo-
quence and the fervid vaticinations of one
who was conspicuous alike by the great-
ness of his rise and the depth of his fall,
drew the attention of all the world to the
'new birth of Time.'

But it is not easy to discover satisfac- The
tory evidence that the ' Novum Organum ' f his

method.

10 THE ADVANCE OP SCIENCE

had any direct beneficial influence on the
advancement of natural knowledge. JSTo
delusion is greater than the notion that
method and industry can make up for
lack of motherwit, either in science or in
practical life ; and it is strange that, with
his knowledge of mankind, Bacon should
have dreamed that his, or any other, ' via
inveniendi scientias' would 'level men's
wits ' and leave little scope for that inborn
capacity which is called genius. As a
matter of fact, Bacon's 'via' has proved
hopelessly impracticable ; while the ' an-
ticipation of nature ' by the invention of
hypotheses based on incomplete induc-
tions, which he specially condemns, has
proved itself to be a most efficient, indeed
an indispensable, instrument of scientific
progress. Finally, that transcendental
alchemy — the superinducement of new
forms on matter — which Bacon declares
to be the supreme aim of science, has
been wholly ignored by those who have

IN THE LAST HALF-CENTURY. 11

created the physical knowledge of the
present day.

Even the eloquent advocacy of the
Chancellor brought no unmixed good to
physical science. It was natural enough
that the man who, in his better moments,
took 'all knowledge for his patrimony,'
but, in his worse, sold that birthright for
the mess of pottage of Court favor and
professional success, for pomp and show,
should be led to attach an undue value to
the practical advantages which he fore-
saw, as Roger Bacon and, indeed, Seneca
had foreseen, long before his time, must
follow in the train of the advancement of
natural knowledge. The burden of Ba-
con' s pleadings for science is the ' gather-
ing of fruit' — the importance of winning-
solid material advantages by the investi-
gation of Nature and the desirableness of
limiting the application of scientific meth-
ods of inquiry to that field.

Bacon's younger contemporary, Hobbes, Hobbes.

12 THE ADVANCE OF SCIENCE

casting aside the prudent reserve of Ms
predecessor in regard to those matters
about which the Crown or the Church
might have something to say, extended
scientific methods of inquiry to the phe-
nomena of mind and the problems of
social organisation ; while, at the same
time, he indicated the boundary between
the province of real, and that of imagi-
nary, knowledge. The ' Principles of Phi-
losophy ' and the ' Leviathan ' embody
a coherent system of purely scientific
thought in language which is a model of
clear and vigorous English style. At the
same time, in France, a man of far greater
scientific capacity than either Bacon or
Des- Hobbes, Rene Descartes, not only in his
immortal 'Discours de la Methode' and
elsewhere, went down to the foundations
of scientific certainty, but, in his 'Prin-
cipes de Philosophic,' indicated where the
goal of physical science really lay. How-
ever, Descartes was an eminent mathema-

IN THE LAST HALF-CENTURY. 13

tician, and it would seem that the bent of
his mind led him to overestimate the value
of deductive reasoning from general prin-
ciples, as much as Bacon had underesti-
mated it. The progress of physical science
has been effected neither by Baconians
nor by Cartesians, as such, but by men
like Galileo and Harvey, Boyle and New-
ton, who would have done their work just
as well if neither Bacon nor Descartes had
ever propounded their views respecting
the manner in which scientific investiga-
tion should be pursued.

The progress of science, during the For a

x ° 53 time the

first century after Bacon's death, by no progress
means verified his sanguine prediction of < fruits.'
the fruits which it would yield. For,
though the revived and renewed study of
nature had spread and grown to an extent
which surpassed reasonable expectation,
the practical results — the 'good to men's
estate' — were, at first, by no means ap-
parent. Sixty years after Bacon's death,

14 THE ADVANCE OF SCIENCE

Newton had crowned the long labors of
the astronomers and the physicists, by co-
ordinating the phenomena of molar mo-
tion throughout the visible universe into
one vast system; but the 'Principia'
helped no man to either wealth or com-
fort. Descartes, Newton, and Leibnitz
had opened up new worlds to the mathe-
matician, but the acquisitions of their
genius enriched only man's ideal estate.
Descartes had laid the foundations of ra-
tional cosmogony and of physiological
psychology ; Boyle had produced models
of experimentation in various branches of
physics and chemistry ; Pascal and Torri-
celli had weighed the air ; Malpighi and
Grew, Ray and Willoughby had done
work of no less importance in the biologi-
cal sciences ; but weaving and spinning
were carried on with the old apjiliances ;
nobody could travel faster by sea or by
land than at any previous time in the
world's history, and King George could

I1N" the last half-century. 15

send a message from London to York no
faster than King John might have done.
Metals were worked from their ores by-
immemorial rule of thumb, and the centre
of the iron trade of these islands was still
among the oak forests of Sussex. The
utmost skill of our mechanicians did not
get beyond the production of a coarse
watch.

The middle of the eighteenth century
is illustrated by a host of great names in
science— English, French, German, and
Italian— especially in the fields of chemis-
try, geology, and biology ; but this deep-
ening and broadening of natural knowl-
edge produced next to no immediate
practical benefits. Even if, at this time,
Francis Bacon could have returned to the
scene of his greatness and of his littleness,
he must have regarded the philosophic
world which praised and disregarded his
precepts with great disfavor. If ghosts
are consistent, he would have said, ' These

16 THE ADVANCE OF SCIENCE

people are all wasting their time, just as
Gilbert and Kepler and Galileo and my
worthy physician Harvey did in my day.
Where are the fruits of the restoration of
science which I promised ? This accumu-
lation of bare knowledge is all very well,
but cui bono ? Not one of these people is
doing what I told him specially to do,
and seeking that secret of the cause of
forms which will enable men to deal, at
will, with matter, and superinduce new
natures upon the old foundations.'
its re- But, a little later, that growth of

feet on knowledge beyond imaginable utilitarian
llfe " ends, which is the condition precedent of
its practical utility, began to produce
some effect upon practical life ; and the
operation of that part of nature we call
human upon the rest began to create, not
'new natures,' in Bacon's sense, but a
new Nature, the existence of which is de-
pendent upon men's efforts, which is sub-
servient to their wants, and which would

IN THE LAST HALF-CENTURY. 17

disappear if man's shaping and guiding
hand were withdrawn. Every mechanical
artifice, every chemically pure substance
employed in manufacture, every abnor-
mally fertile race of plants, or rapidly
growing and fattening breed of animals,
is a part of the new Nature created by sci-
ence. Without it, the most densely popu-
lated regions of modern Europe and Amer-
ica must retain their primitive, sparsely
inhabited, agricultural or pastoral con-
dition ; it is the foundation of our wealth
and the condition of our safety from sub-
mergence by another flood of barbarous
hordes ; it is the bond which unites into a
solid political whole, regions larger than
any empire of antiquity; it secures us
from the recurrence of the pestilences and
famines of former times ; it is the source
of endless comforts and conveniences,
which are not mere luxuries, but conduce
to physical and moral well-being. Dur-
ing the last fifty years, this new birth of

18 THE ADVANCE OF SCIENCE

time, this new Nature begotten by science
upon fact, has pressed itself daily and
hourly upon our attention, and has
worked miracles which have modified the
whole fashion of our lives.
These What wonder, theu, if these astonish-

often too ing fruits of the tree of knowledge are too
gardedT 0I " tei1 regarded by both friends and ene-
mies as the be-all and end-all of science ?
What wonder if some eulogise, and others
revile, the new philosophy for its utilita-
rian ends and its merely material tri-
umphs ?
forscien- In truth, the new philosophy deserves
search" neither the praise of its eulogists, nor the
blame of its slanderers. As I have point-
ed out, its disciples were guided by no
search after practical fruits, during the
great period of its growth, and it reached
adolescence without being stimulated by
any rewards of that nature. The bare
enumeration of the names of the men who
were the great lights of science in the lat-

IN THE LAST HALF-CEXTURY. 19

ter part of the eighteenth and the first de-
cade of the nineteenth century, of Her-
schel, of Laplace, of YouDg, of Fresnel,
of Oersted, of Cavendish, of Lavoisier, of
Davy, of Lamarck, of Cuvier, of Jussien,
of Decandolle, of Werner and of Hutton,
suffices to indicate the strength of physi-
cal science in the age immediately preced-
ing that of which I have to treat. But of
which of these great men can it be said
that their labors were directed to practi-
cal ends ? I do not call to mind even an rarely

t . i directed

invention of practical utility which we to prac-
owe to any of them, except the safety- e ^ dgj
lamp of Davy. Werner certainly paid
attention to mining, and I have not for-
gotten James Watt. But, though some
of the most important of the improve-
ments by which Watt converted the
steam-engine, invented long before his
time, into the obedient slave of man, were
suggested and gnided by his acquaintance
with scientific principles, his skill as a

20 THE ADVANCE OF SCIENCE

practical mechanician, and the efficiency
of Bolton's workmen had quite as much
to do with the realisation of his pro-
jects.
but in- In fact, the history of physical science

byfoveof teaches (and we cannot too carefully take
edge! 1 " ^ e l esson to heart) that the practical ad-
vantages, attainable through its agency,
never have been, and never will be, suffi-
ciently attractive to men inspired by the
inborn genius of the interpreter of nature,
to give them courage to undergo the toils
and make the sacrifices which that calling
requires from its votaries. That which
stirs their pulses is the love of knowledge
and the joy of the discovery of the causes
of things sung by the old poets — the su-
preme delight of extending the realm of
law and order ever farther towards the
unattainable goals of the infinitely great
and the infinitely small, between which
our little race of life is run. In the
course of this work, the physical philoso-

IN THE LAST HALF-CENTUEY. 21

plier, sometimes intentionally, much more
often unintentionally, lights upon some-
thing which proves to be of practical
value. Great is the rejoicing of those
who are benefited thereby ; and, for the
moment, science is the Diana of all the
craftsmen. But, even while the cries of
jubilation resound and this floatsam and
jetsam of the tide of investigation is be-
ing turned into the wages of workmen and
the wealth of capitalists, the crest of the
wave of scientific investigation is far away
on its course over the illimitable ocean of
the unknown.

Far be it from me to depreciate the
value of the gifts of science to practical
life, or to cast a doubt upon the propriety
of the course of action of those who follow
science in the hope of finding wealth along-
side truth, or even wealth alone. Such a
profession is as respectable as any other.
And quite as little do I desire to ignore it is, in

. „ . ^ i its turn,

the fact that, if industry owes a heavy ass i st ed

ments.

22 THE ADVANCE OF SCIENCE

by in- debt to science, it lias largely repaid the
improve- loan by the important aid which it has, in
its turn, rendered to the advancement of
science. In considering the causes which
hindered the progress of physical knowl-
edge in the schools of Athens and of Alex-
andria, it has often struck me * that where
the Greeks did wonders was in just those
branches of science, such as geometry,
astronomy, and anatomy, which are sus-
ceptible of very considerable development
without any, or any but the simplest, ap-
pliances. It is a curious speculation to
think what would have become of modern
physical science if glass and alcohol had
not been easily obtainable ; and if the
gradual perfection of mechanical skill for
industrial ends had not enabled investi-
gators to obtain, at comparatively little

* There are excellent remarks to the same effect in
Zeller's Philosopllie der Gricchen, Theil II. Abth. ii.
p. 407, and in Eucken's DieMethodeder Aristotelischen,
Forscliung, pp. 138 et seq.

IN THE LAST HALF- CENTURY. 23

cost, microscopes, telescopes, and all the
exquisitely delicate apparatus for deter-
mining weight and measure and for esti-
mating the lapse of time with exactness,
which they now command. If science has
rendered the colossal development of mod-
ern industry possible, beyond a doubt in-
dustry has done no less for modern phys-
ics and chemistry, and for a great deal of
modern biology. And as the captains of
industry have, at last, begun to be aware
that the condition of success in that war-
fare, under the forms of peace, which is
known as industrial competition lies in
the discipline of the troops and the use of
arms of precision, just as much as it does
in the warfare which is called war, their
demand for that discipline, which is tech-
nical education, is reacting upon science
in a manner which will, assuredly, stimu-
late its future growth to an incalculable
extent. It has become obvious that the
interests of science and of industry are

24 THE ADVANCE OF SCIENCE

identical ; that science cannot make a step
forward without, sooner or later, opening
up new channels for industry ; and, on
the other hand, that every advance of in-
dustry facilitates those experimental in-
vestigations, upon which the growth of
science depends. We may hope that, at
last, the weary misunderstanding between
the practical men who professed to despise
science, and the high and dry philoso-
phers w T ho professed to despise practical
results, is at an end.

Nevertheless, that which is true of the
infancy of physical science in the Greek
world, that which is true of its adoles-
cence in the seventeenth and eighteenth
centuries, remains true of its riper age in
these latter days of the nineteenth cent-
ury. The great steps in its progress have
been made, are made, and will be made,
by men who seek knowledge simply be-
cause they crave for it. They have their
weaknesses, their follies, their vanities,

IN THE LAST HALF-CEISTTTJEY. 25

and their rivalries, like the rest of the
world; but whatever by-ends may mar
their dignity and impede their usefulness,
this chief end redeems them.* Nothing
great in science has ever been done by
men, whatever their powers, in whom the
divine afflatus of the truth -seeker was
wanting. Men of moderate capacity have
done great things because it animated

* Fresnel, after a brilliant career of discovery in
some of the most difficult regions of physico-inathe-
matical science, died at thirty-nine years of age. The
following passage of a letter from him to Young
(written in November 1824), quoted by Whewell, so
aptly illustrates the spirit which animates the scientific
inquirer that I may cite it :

'For a long time that sensibility, or that vanity,
which people call love of glory is much blunted in me.
I labor much less to catch the suffrages of the public
than to obtain an inward approval which has always
been the mental reward of my efforts. Without doubt
I have often wanted the spur of vanity to excite me to
pursue my researches in moments of disgust and dis-
couragement. But all the compliments which I have
received from MM. Arago, De Laplace, or Biot, never
gave me so much pleasure as the discovery of a theo-
retical truth or the confirmation of a calculation by ex-
periment.'

26 THE ADVANCE OF SCIENCE

them ; and men of great natural gifts have
failed, absolutely or relatively, because
they lacked this one thing needful.
Traeaim To anyone who knows the business of
method investigation practically, Bacon's notion of
search, establishing a company of investigators to
work for 'fruits,' as if the pursuit of
knowledge were a kind of mining operation
and only required well-directed picks and
shovels, seems very strange." In science,
as in art, and, as I believe, in every other
sphere of human activity, there may be
wisdom in a multitude of counsellors, but
it is only in one or two of them. And, in
scientific inquiry, at any rate, it is to that
one or two that we must look for light
and guidance. Xewton said that he made
his discoveries by 'intending' his mind

* 'Memorable exemple de l'impuissance des recher-
ches collectives appliquees a la dticouverte des v6rites
nouvelles! ' says one of the most distinguished of living
French savants, of the corporate chemical work of the
old Academie des Sciences. (See Berthelot, Science et
Philosophic, p. 201.)

IN THE LAST HALF- CENTURY. 27

on the subject ; no doubt truly. But to
equal his success one must have the mind
which he 'intended.' Forty lesser men
might have intended their minds till they
cracked, without any like result. It
would be idle either to affirm or to deny
that the last half-century has produced
men of science of the calibre of Newton.
It is sufficient that it can show a few ca-
pacities of the first rank, competent not
only to deal profitably with the inheritance
bequeathed by their scientific forefathers,
but to pass on to their successors physical
truths of a higher order than any yet
reached by the human race. And if they
have succeeded as Newton succeeded, it
is because they have sought truth as he
sought it, with no other object than the
finding it.

I am conscious that in undertaking to Progress

„ , from

give even the briefest sketch ot the prog- iss: to
ress of physical science, in all its branches.

28 THE ADVANCE OF SCIENCE

during the last half - century, I may be
thought to have exhibited more courage
than discretion, and perhaps more pre-
sumption than either. So far as physical
science is concerned, the days of Admi-
rable Crichtons have long been over, and
the most indefatigable of hard workers
may think he has done well if he has
mastered one of its minor subdivisions.
Nevertheless, it is possible for anyone,
who has familiarised himself with the
operations of science in one department,
to comprehend the significance, and even
to form a general estimate of the value, of
the achievements of specialists in other
departments.

JNor is their any lack either of guidance,
or of aids to ignorance. By a happy chance,
the first edition of Whewell's 'History
of the Inductive Sciences' was published
in 1837, and it affords a very useful view
of the state of things at the commence-
ment of the Victorian epoch. As to sub-

m THE LAST HALF-CENTURY. 29

sequent events, there are numerous excel-
lent summaries of the progress of various
branches of science, especially up to 1881,
which was the jubilee year of the British
Association. * And, with respect to the
biological sciences, with some parts of
which my studies have familiarised me,
my personal experience nearly coincides
with the preceding half-century. I may
hope, therefore, that my chance of escap-
ing serious errors is as good as that of
anyone else, who might have been per-
suaded to undertake the somewhat peri-
lous enterprise in which I find myself
engaged.

There is yet another prefatory remark
which it seems desirable I should make.
It is that I think it proper to confine my-
self to the work done, without saying any-

* I am particularly indebted to my friend and col-
league Professor Riicker, F. R. S., for the many acute
criticisms and suggestions on ray remarks respecting
the ultimate problems of physics, with which he has
favored me, and by which I have greatly profited.

30 THE ADVANCE OF SCIENCE

thing about the doers of it. Meddling
with questions of merit and priority is a
thorny business at the best of times, and
unless in case of necessity, altogether un-
desirable when one is dealing with con-
temporaries. No such necessity lies upon
me ; and I shall, therefore, mention no
names of living men, lest, perchance, I
should incur the reproof which the Is-
raelites, who struggled with one an-
other in the field, addressed to Moses —
'Who made thee a prince and a judge
over us \ '

The aim Physical science is one and indivisible.

of phvs- . .

ical sei- Although, tor practical purposes, it is
convenient to mark it out into the pri-
mary regions of Physics, Chemistry, and
Biology, and to subdivide these into sub-
ordinate provinces, yet the method of
investigation and the ultimate object of
the physical inquirer are everywhere the
same.

ITT THE LAST HALF-CENTUEY. 31

The object is the discovery of the ra- the dis-

d , covery

tional order which pervades the universe ; of the

. , ,. -j rational

the method consists of observation and order of
experiment (which is observation under T€ J£ m "
artificial conditions) for the determination
of the facts of nature ; of inductive and
deductive reasoning for the discovery of
their mutual relations and connection.
The various branches of physical science
differ in the extent to which, at any given
moment of their history, observation on
the one hand, or ratiocination on the other,
is their more obvious feature, but in no
other way ; and nothing can be more in-
correct than the assumption one sometimes
meets with, that physics has one method,
chemistry another, and biology a third.

All physical science starts from cer- It is
tain postulates. One of them is the ob- onpos-
jective existence of a material world. It a '
is assumed that the phenomena which are
comprehended under this name have a
'substratum' of extended, impenetrable,

32 THE ADVANCE OF SCIENCE

mobile substance, which exhibits the qual-
ity known as inertia, and is termed mat-
ter.* Another postulate is the univer-
sality of the law of causation ; that noth-
ing happens without a cause (that is, a
necessary precedent condition), and that
the state of the physical universe, at any
given moment, is the consequence of its

* I am aware that this proposition may be chal-
lenged. It may be said, for example, that, on the hy-
pothesis of Boscovicb, matter has no extension, being
reduced to mathematical points serving as centres of
' forces. 1 But as the ' forces ' of the various centres
are conceived to limit one another's action in such a
manner that an area around each centre has an indi-
viduality of its own, extension comes back in the form
of that area. Again, a very eminent mathematician
and physicist — the late Clerk Maxwell — has declared
that impenetrability is not essential to our notions of
matter, and that two atoms may conceivably occupy
the same space. I am loth to dispute any dictum of a
philosopher as remarkable for the subtlety of his in-
tellect as for his vast knowledge; but the assertion
that one and the same point or area of space can have
different (conceivably opposite) attributes appears to
me to violate the principle of contradiction, which is
the foundation not only of physical science, but of
logic in general. It means that A can be not- A.

m THE LAST IIALF-OENTUEY. 33

state at any preceding moment. Another
is that any of the rules, or so-called ' laws
of nature,' by which the relation of phe-
nomena is truly denned, is true for all
time. The validity of these postulates
is a problem of metaphysics ; they are
neither self-evident nor are they, strict-
ly speaking, demonstrable. The justifica-
tion of their employment, as axioms of
physical philosophy, lies in the circum-
stance that expectations logically based
upon them are verified, or, at any rate,
not contradicted, whenever they can be
tested by experience.

Physical science therefore rests on veri- and uses

J hypoth-

fied or uncontradicted hypotheses ; and, escs.
such being the case, it is not surprising
that a great condition of its progress has
been the invention of verifiable hypothe-
ses. It is a favorite popular delusion
that the scientific inquirer is under a sort
of moral obligation to abstain from going
beyond that generalisation of observed

3

34 THE ADVANCE OF SCIENCE

facts which is absurdly called ' Baconian '
induction. But anyone who is practically
acquainted with scientific work is aware
that those who refuse to go beyond fact,
rarely get as far as fact ; and anyone who
has studied the history of science knows
that almost every great step therein has
been made by the 'anticipation of Na-
ture,' that is, by the invention of hy-
potheses, which, though verifiable, often
had very little foundation to start with ;
and, not unfrequently, in spite of a long
career of usefulness, turned out to be
wholly erroneous in the long run.
Fruitful The geocentric system of astronomy,

use of an .

hypoth- with its eccentrics and its epicycles, was
wien a n hypothesis utterly at variance with
wrong, £ ac ^ w j 1 j c ] 1 nevertheless did great things
for the advancement of astronomical
knowledge. Kepler was the wildest of
guessers. Newton's corpuscular theory
of light was of much temporary use in
optics, though nobody now believes in it ;

IN THE LAST HALF-CENTURY. 35

and the undulatory theory, which has
superseded the corpuscular theory and
has proved one of the most fertile of in-
struments of research, is based on the
hypothesis of the existence of an ' ether,'
the properties of which are denned in
propositions, some of which, to ordinary
apprehension, seem physical antinomies.
It sounds paradoxical to say that the
attainment of scientific truth has been
effected, to a great extent, by the help of
scientific errors. But the subject-matter
of physical science is furnished by obser-
vation, which cannot extend beyond the
limits of our faculties ; while, even within
those limits, we cannot be certain that
any observation is absolutely exact and
exhaustive. Hence it follows that any
given generalisation from observation may
be true, within the limits of our powers
of observation at a given time, and yet
turn out to be untrue, when those powers
of observation are directly or indirectly

36 THE ADVANCE OF SCIENCE

enlarged. Or, to put the matter in an-
other way, a doctrine which is untrue ab-
solutely, may, to a very great extent, be
susceptible of an interpretation in accord-
ance with the truth. At a certain period
in the history of astronomical science, the
assumption that the planets move in cir-
cles was true enough to serve the purpose
of correlating such observations as were
then possible ; after Kepler, the assump-
tion that they move in ellipses became
true enough in regard to the state of ob-
servational astronomy at that time. TVe
say still that the orbits of the planets
are ellipses, because, for all ordinary pur-
poses, that is a sufficiently near approxi-
mation to the truth; but, as a matter of
fact, the centre of gravity of a planet de-
scribes neither an ellipse or any other
simple curve, but an immensely compli-
cated undulating line. It may fairly be
doubted whether any generalisation, or
hypothesis, based upon physical data is

IN THE LAST HALF-CEXTUEY. 37

absolutely true, in the sense that a mathe-
matical proposition is so ; but, if its errors
can become apparent only outside the
limits of practicable observation, it may
be just as usefully adopted for one of the
symbols of that algebra by which we in-
terpret nature, as if it were absolutely
true.

The development of every branch of
physical knowledge presents three stages
which, in their logical relation, are suc-
cessive. The first is the determination of
the sensible character and order of the
phenomena. This is Natural History, in
the original sense of the term, and here
nothing but observation and experiment
avail us. The second is the determination
of the constant relations of the phenomena
thus defined, and their expression in rules
or laws. The third is the explication of
these particular laws by deduction from
the most general laws of matter and mo-
tion. The last two stages constitute Nat-

38 THE ADVANCE OF SCIENCE

ural PJiilosophy in its original sense. In
this region, the invention of verifiable
hypotheses is not only permissible, but is
one of the conditions of progress,
and mu- Historically, no branch of science has

tual as-
sistance followed this order of growth ; but, from

vation, the dawn of exact knowledge to the pres-

ment 1 " en * ^Ti observation, experiment, and

and speculation have gone hand in hand ; and,

whenever science has halted or strayed

from the right path, it has been, either

specula- because its votaries have been content

with mere unverified or unverifiable spec-

I ulation (and this is the commonest case,

because observation and experiment are

hard work, while speculation is amusing) ;

or it has been, because the accumulation

of details of observation has for a time

excluded speculation.

Recogni- The progress of physical science, since

these° the revival of learning, is largely due to

recent m * n e ^ ac ^ tna ^ men nave gradually learned

times, j i a y as i(j e the consideration of unverifia-

IN THE LAST IIALF-CEXTURY. 39

ble hypotheses ; to guide observation and
experiment by verifiable hypotheses ; and
to consider the latter, not as ideal truths,
the real entities of an intelligible world be-
hind phenomena, but as a symbolical lan-
guage, by the aid of which nature can be
interpreted in terms apprehensible by our
intellects. And if physical science, dur- and con-

i n p i -i • sequent

mg the last nlty years, has attained di- progress,
mensions beyond all former precedent,
and can exhibit achievements of greater
importance than any former such period
can show, it is because able men, ani-
mated by the true scientific spirit, care-
fully trained in the method of science,
and having at their disposal immensely
improved appliances, have devoted them-
selves to the enlargement of the bounda-
ries of natural knowledge in greater num-
ber than during any previous half-century
of the world's history.

I have said that our epoch can produce The
achievements in physical science of great- g^

40 THE ADVANCE OF SCIENCE

achieve- er moment than any other has to show,

merits

Doc- advisedly ; and I think that there are

(IJmo- three great products of our time which

constitu- J us tify the assertion. One of these is that

tion of doctrine concerning the constitution of

matter,

(2) con- matter which, for want of a better name,

SCrVcl -

tion of I will call ' molecular ; ' the second is the
(3) e eV Qiu- doctrine of conservation of energy ; the
tion. third is the doctrine of evolution. Each
of these was foreshadowed, more or less
distinctly, in former periods of the his-
tory of science ; and, so far is either from
being the outcome of purely inductive
reasoning, that it would be hard to over- }
rate the influence of metaphysical, and
even of theological, considerations upon
the development of all three. The pe-
culiar merit of our epoch is that it has
shown how these hypotheses connect a
vast number of seemingly independent
partial generalisations ; that it has given
them that precision of expression which ,
is necessary for their exact verification;

IN THE LAST HALF-CENTUKY. 41

and that it has practically proved their
value as guides to the discovery of new
truth. All three doctrines are intimately
connected, and each is applicable to the
whole physical cosmos. But, as might
have been expected from the nature of
the case, the first two grew, mainly, out
of the consideration of physico-chemical
phenomena ; while the third, in great
measure, owes its rehabilitation, if not
its origin, to the study of biological phe-
nomena.

In the early decades of this century, a (l) Mo-
number of important truths applicable, in constitu-
part, to matter in general, and, in part, matter.
to particular forms of matter, had been
ascertained by the physicists and chem-
ists.

The laws of motion of visible and tan-
gible, or molar, matter had been worked
out to a great degree of refinement and
embodied in the branches of science

42 THE ADVANCE OF SCIENCE

known as Mechanics, Hydrostatics, and
Pneumatics. These laws had been shown
to hold good, so far as they could be
checked by observation and experiment,
throughout the universe, on the assump-
tion that all such masses of matter pos-
sessed inertia and were susceptible of ac-
quiring motion, in two ways, firstly by
impact, or impulse from without ; and,
secondly, by the operation of certain
hypothetical causes of motion termed
'forces,' which were usually supposed to
be resident in the particles of the masses
themselves, and to operate at a distance,
in such a way as to tend to draw any two
such masses together, or to separate them
more widely.
The two With respect to the ultimate constitu-
te to tion of these masses, the same two antago-
matter. n ^j c pi n i ons which had existed since
the time of Democritus and of Aristotle
were still face to face. According to the
one, matter was discontinuous and con-

IX THE LAST HALF-CENTURY. 43

sisted of minute indivisible particles or
atoms, separated by a universal vacuum ;
according to the other, it was continuous,
and the finest distinguishable, or imagina-
ble, particles were scattered through the
attenuated general substance of the ple-
num. A rough analogy to the latter case
would be afforded by granules of ice dif-
fused through water ; to the former, such
granules diffused through absolutely emp-
ty space.

In the latter part of the eighteenth
century, the chemists had arrived at sev-
eral very important generalisations re-
specting those properties of matter with
which they were especially concerned.
However plainly ponderable matter
seemed to be originated and destroyed in
their operations, they proved that, as
mass or body, it remained indestructible
and ingenerable ; and that, so far, it va-
ried only in its perceptibility by our
senses. The course of investigation fur-

44 THE ADVANCE OF SCIENCE

ther proved that a certain number of the
chemically separable kinds of matter were
"unalterable by any known means (ex-
cept in so far as they might be made to
change their state from solid to fluid, or
vice versa), unless they were brought into
contact with other kinds of matter, and
that the properties of these several kinds
of matter were always the same, whatever
their origin. All other bodies were found
to consist of two or more of these, which
thus took the place of the four ' elements '
of the ancient philosophers. Further, it
was proved that, in forming chemical com-
pounds, bodies always unite in a definite
proportion by weight, or in simple multi-
ples of that proportion, and that, if any
one body were taken as a standard, every
other could have a number assigned to it
Reasser- as its proportional combining weight. It
Daiton was on this foundation of fact that Dal-
theoryl 10 ton based his re-establishment of the old
atomic hypothesis on a new empirical

IN THE LAST HALF-CEXTURY. 45

foundation. It is obvious, that if ele-
mentary matter consists of indestructible
and indivisible particles, each of which
constantly preserves the same weight rela-
tively to all the others, compounds formed
by the aggregation of two, three, four, or
more such particles must exemplify the
rule of combination in definite proportions
deduced from observation.

In the meanwhile, the gradual recep-
tion of the undulatory theory of light ne-
cessitated the assumption of the existence
of an ' ether ' filling all space. But
whether this ether was to be regarded as
a strictly material and continuous sub-
stance was an undecided point, and hence
the revived atomism escaped strangling
in its birth. For it is clear, that if the
ether is admitted to be a continuous ma-
terial substance, Democritic atomism is
at an end and Cartesian continuity takes
its place.

The real value of the new atomic hy- The red

46 THE ADVANCE OF SCIENCE

value of pothesis, however, did not lie in the two
pothesis; points which Democritus and his followers
would have considered essential — namely,
the indivisibility of the 'atoms' and the
presence of an interatomic vacuum — but
in the assumption that, to the extent to
which our means of analysis take us, ma-
it prcdi- terial bodies consist of definite minute

cates the , „ -, . -, j. -i • i

cx i s t- masses, each of which, so iar as physical
units°of an< ^ chemical processes of division go,
matter. ma y ^ e re g ar d e d as a unit — having a

practically permanent individuality. Just
as a man is the unit of sociology, without
reference to the actual fact of his divisi-
bility, so such a minute mass is the unit
of physico-chemical science — that small-
est material particle which under any
given circumstances acts as a whole.*
The doctrine of specific heat originated

* ' Molecule ' would be the more appropriate name
for such a particle. Unfortunately, chemists employ
this term in a special sense, as a name for an aggrega-
tion of their smallest particles, for which they retain
the designation of 'atoms.'

IN THE LAST HALF-CENTURY. 47

in the eighteenth century. It means that
the same mass of a body, under the same
circumstances, always requires the same
quantity of heat to raise it to a given
temperature, but that equal masses of
different bodies require different quanti-
ties. Ultimately, it was found that the
quantities of heat required to raise equal
masses of the more perfect gases, through
equal ranges of temperature, were in-
versely proportional to their combining
weights. Thus a definite relation was es-
tablished between the hypothetical units
and heat. The phenomena of electrolytic
decomposition showed that there was a
like close relation between these units and
electricity. The quantity of electricity
generated by the combination of any two
units is sufficient to separate any other
two which are susceptible of such decom-
position. The phenomena of isomorph-
ism showed a relation between the units
and crystalline forms ; certain units are

48 THE ADVANCE OF SCIENCE

thus able to replace others in a crystalline
body without altering its form, and others
are not.

Again, the laws of the effect of press-
ure and heat on gaseous bodies, the fact
that they combine in definite proportions
by volume, and that such proportion
bears a simple relation to their combining
weights, all harmonised with the Dalto-
nian hypothesis, and led to the bold
speculation known as the law T of Avoga-
dro — that all gaseous bodies, under the
same physical conditions, contain the
same number of units. In the form in
which it was first enunciated, this hy-
pothesis was incorrect— jjerhaps it is not
exactly true in any form ; but it is hardly
too much to say that chemistry and mo-
lecular physics would never have ad-
vanced to their present condition unless
it had been assumed to be true. Another
immense service rendered by Dalton, as a
corollary of the new atomic doctrine,

IN THE LAST HALF-CENTURY. 49

was the creation of a system of symbolic
notation, which not only made the nature
of chemical compounds and processes eas-
ily intelligible and easy of recollection,
but, by its very form, suggested new lines
of inquiry. The atomic notation was as
serviceable to chemistry as the binomial
nomenclature and the classificatory sche-
matism of Linnseus were to zoology and
botany.

Side by side with these advances arose in biolo-
another, which also has a close parallel in fheoryof
the history of biological science. If the Srstnic-
unit of a compound is made up by the ture *
aggregation of elementary units, the no-
tion that these must have some sort of
definite arrangement inevitably suggests
itself ; and such phenomena as double de-
composition pointed, not only to the ex-
istence of a molecular architecture, but to
the possibility of modifying a molecular
fabric without destroying it, by taking
out some of the component units and

50 THE ADVANCE OE SCIENCE

replacing them by others. The class of
neutral salts, for example, includes a
great number of bodies in many ways
similar, in which the basic molecules, or
the acid molecules, may be replaced by
other basic and other acid molecules with-
out altering the neutrality of the salt ;
just as a cube of bricks remains a cube,
so long as any brick that is taken out is
replaced by another of the same shape
and dimensions, whatever its weight or
other properties may be. Facts of this
kind gave rise to the conception of
'types' of molecular structure, just as
the recognition of the unity in diversity
of the structure of the species of plants
and animals gave rise to the notion of
biological ' types.' The notation of chem-
istry enabled these ideas to be repre-
sented with precision ; and they acquired
an immense importance, when the im-
X)rovement of methods of analysis, which
took place about the beginning of our

IN THE LAST HALF-CENTURY. 61

period, enabled the composition of the so-
called 'organic' bodies to be determined
with rapidity and precision.* A large
proportion of these componnds contain
not more than three or fonr elements, of
which carbon is the chief ; bnt their num-
ber is very great, and the diversity of
their physical and chemical properties is
astonishing. The ascertainment of the
proportion of each element in these com-
pounds affords little or no help towards
accounting for their diversities ; widely
different bodies being often very similar,
or even identical, in that respect. And,
in the last case, that of isomeric com-
pounds, the appeal to diversity of ar-
rangement of the identical component
units was the only obvious way out of
the difficulty. Here, again, hypothesis

* ' At present more organic analyses are made in a
single day than were accomplished before Liebig's
time in a wbole year.' — Hofmann, Faraday Lecture,
p. 46.

52 THE ADVANCE OF SCIEXCE

proved to be of great value ; not only was
the search for evidence of diversity of
molecular structure successful, but the
study of the process of taking to pieces
led to the discovery of the way to put to-
gether ; and vast numbers of compounds,
some of them previously known only as
products of the living economy, have thus
been artificially constructed. Chemical
work, at the present day, is, to a large
extent, synthetic or creative — that is to
say, the chemist determines, theoretical-
ly, that certain non-existent compounds
ought to be producible, and he proceeds
to produce them.

It is largely because the chemical the-
ory and practice of our epoch have passed
into this deductive and synthetic stage,
that they are entitled to the name of the
'New Chemistry' which they commonly
receive. But this new chemistry has
grown up by the help of hypotheses, such
as those of Dalton and of Avogadro, and

IN THE LAST HALF-CENTUBY. 53

that singular conception of 'bonds' in-
vented to colligate the facts of 'valency'
or 'atomicity,' the first of which took
some time to make its way ; while the
second fell into oblMon, for many years
after it was propounded, for lack of em-
pirical justification. As for the third, it
may be doubted if anyone regards it as
more than a temporary contrivance.

But some of these hypotheses have
done yet further service. Combining
them with the mechanical theory of heat
and the doctrine of the conservation of
energy, which are also products of our
time, physicists have arrived at an entire-
ly new conception of the nature of gaseous
bodies and of the relation of the physico-
chemical units of matter to the different
forms of energy. The conduct of gases
under varying pressure and temperature,
their diffusibility, their relation to radiant
heat and to light, the evolution of heat
when bodies combine, the absolution of

54 THE ADVANCE OF SCIENCE

heat when they are dissociated, and a
host of other molecular phenomena, have
been shown to be deducible from the dy-
namical and statical principles which ap-
ply to molar motion and rest ; and the
tendency of physico-chemical science is
clearly towards the reduction of the prob-
lems of the world of the infinitely little,
as it already has reduced those of the in-
finitely great world, to questions of me-
chanics. *

In the meanwhile, the primitive atomic
theory, which has served as the scaffold-
ing for the edifice of modern physics and
chemistry, has been quietly dismissed. I
cannot discover that any contemporary
physicist or chemist believes in the real
indivisibility of atoms, or in an inter-
atomic matterless vacuum. 'Atoms' ap-

* In the preface to his Mecanique Chimique M.
Berthelot declares his object to be ' ramener la chimie
tout entiere . . . aux m&mes principes mecaniques qui
regissent deja les diverses branches de la physique.'

IN THE LAST HALF- CENTURY. 55

pear to be used as mere names for physico-
chemical units which have not yet been
subdivided, and 'molecules' for physico-
chemical units which are aggregates of
the former. And these individualised
particles are supposed to move in an end-
less ocean of a vastly more subtle matter
—the ether. If this ether is a continuous
substance, therefore, we have got back
from the hypothesis of Dalton to that of
Descartes. But there is much reason to
believe that science is going to make a
still further journey, and, in form, if not
altogether in substance, to return to the
point of view of Aristotle.

The greater number of the so-called Eie-

, , ,. , t ^ mentary

'elementary' bodies, now known, had bodies
been discovered before the commencement
of our epoch ; and it had become appar-
ent that they were by no means equally
similar or dissimilar, but that some of
them, at any rate, constituted groups, the
several members of which were as much

56 THE ADVANCE OF SCIENCE

like one another as they were unlike the
rest. Chlorine, iodine, bromine, and flu-
orine thus formed a very distinct group ;
sulphur and selenium another ; boron and
silicon another ; potassium, sodium, and
lithium another; and so on. In some
cases, the atomic weights of such allied
bodies were nearly the same, or could be
arranged in series, with like differences
between the several terms. In fact, the
elements afforded indications that they
were susceptible of a classification in nat-
ural groups, such as those into which ani-
mals and plants fall.
fall into Recently this subject has been taken

different . ., . , .

series. up airesh, with a result which may be
stated roughly in the following terms : If
the sixty-five or sixty-eight recognised
'elements' are arranged in the order of
their atomic weights — from hydrogen, the
lightest, as unity, to uranium, the heavi-
est, as 240— the series does not exhibit
one continuous progressive modification

IN THE LAST HALF-CENTURY. 57

in the physical and chemical characters of
its several terms, but breaks up into a
number of sections, in each of which the
several terms present analogies with the
corresponding terms of the other series.
Thus the whole series does not run

a, b, c, d, e,f, g, 7i, i, Jc, &c,
but

a, b, e, d, a, b, c, d, a, (3, 7, S, &c. ;

so that it is said to express aperiodic law
of recurrent similarities. Or the relation
may be expressed in another way. In
each section of the series, the atomic
weight is greater than in the preceding-
section, so that if 10 is the atomic weight
of any element in the first segment, w + x
will represent the atomic weight of any
element in the next, and w + x + y the
atomic weight of any element in the next,
and so on. Therefore the sections may
be represented as parallel series, the cor-
responding terms of which have analo-

58 THE ADVANCE OF SCIENCE

gous properties ; each, successive series
starting with a body the atomic weight of
which is greater than that of any in the
preceding series, in the following fashion :

d

D

8

c

C

7

b

B

/3

a

A

a

w

W + X

w + x + y

This is a conception with which biolo-
gists are very familiar, animal and plant
groups constantly appearing as series of
parallel modifications of similar and yet
different primary forms. In the living
world, facts of this kind are now under-
stood to mean evolution from a common
prototype. It is difficult to imagine that
The pos- in the not-living world they are devoid of
Sa y significance. Is it not possible, nay prob-
form a oY able, that they may mean the evolution of
matter. our < e i emen t s ' from a primary undifferen-

IN THE LAST HALF-CENTURY. 59

tiated form of matter \ Fifty years ago,
such a suggestion would have been
scouted as a revival of the dreams of the
alchemists. At present, it may be said to
be the burning question of physico-chemi-
cal science.

In fact, the so-called 'vortex-ring' hy-
pothesis is a very serious and remarkable
attempt to deal with material units from a
point of view which is consistent with the
doctrine of evolution. It supposes the
ether to be a uniform substance, and that
the ' elementary ' units are, broadly speak-
ing, permanent whirlpools, or vortices, of
this ether, the properties of which depend
on their actual and potential modes of
motion. It is curious and highly inter-
esting to remark that this hypothesis re-
minds us not only of the speculations of
Descartes, but of those of Aristotle. The
resemblance of the 'vortex-rings' to the
' tourbillons ' of Descartes is little more
than nominal ; but the correspondence be-

60 THE ADVANCE OP SCIENCE

tween the modern and the ancient notion
of a distinction between primary and de-
rivative matter is, to a certain extent,
real. For this ethereal 'Urstoff' of the
modern corresponds very closely with the
7rpa>T7) v\t) of Aristotle, the materia prima
of his mediseval followers ; while matter,
differentiated into our elements, is the
equivalent of the first stage of progress
towards the ia-xarrj vXtj, or finished matter,
of the ancient philosophy.

If the material units of the existing
order of nature are specialised portions of
a relatively homogeneous materia prima
— which were originated under conditions
that have long ceased to exist and which
remain unchanged and unchangeable un-
der all conditions, whether natural or ar-
tificial, hitherto known to us — it follows
that the speculation that they may be
indefinitely altered, or that new units may
be generated under conditions yet to be
discovered, is perfectly legitimate. The-

IX THE LAST HALF-CENTURY. 61

oretically, at any rate, the transmutability
of the elements is a verifiable scientific
hypothesis ; and such inquiries as those
which have been set afoot, into the possi-
ble dissociative action of the great heat of
the sun upon our elements, are not only
legitimate, but are likely to yield results
which, whether affirmative or negative,
will be of great importance. The idea
that atoms are absolutely ingenerable and
immutable ' manufactured articles ' stands
on the same sort of foundation as the idea
that biological species are 'manufactured
articles ' stood thirty years ago ; and the
supposed constancy of the elementary
atoms, during the enormous lapse of time
measured by the existence of our uni-
verse, is of no more weight against the
possibility of change in them, in the in-
finity of antecedent time, than the con-
stancy of species in Egypt, since the days
of Rameses or Cheops, is evidence of their
immutability during all past epochs of

62 THE ADVANCE OF SCIENCE

the earth's history. It seems safe to
prophesy that the hypothesis of the evo-
lution of the elements from a primitive
matter will, in future, play no less a part
in the history of science than the atomic
hypothesis, which, to begin with, had no
greater, if so great, an empirical founda-
tion.
The old It may perhaps occur to the reader

new that the boasted progress of physical sci-
theorv. ence does not come to much, if our pres-
ent conceptions of the fundamental nature
of matter are expressible in terms em-
ployed, more than two thousand years
ago, by the old 'master of those that
know.' Such a criticism, however, would
involve forgetfulness of the fact, that the
* connotation of these terms, in the mind of
the modern, is almost infinitely different
from that which they possessed in the
mind of the ancient, philosopher. In
antiquity, they meant little more than
vague speculation ; at the present day,

IN" THE LAST HALF-CEXTUEY. 63

they indicate definite physical concep-
tions, susceptible of mathematical treat-
ment, and giving rise to innumerable
deductions, the value of which can be
experimentally tested. The old notions
produced little more than floods of dia-
lectics ; the new are powerful aids to-
wards the increase of solid knowledge.

Everyday observation shows that, of ( 2 ) Con -

J J ' serva-

the bodies which compose the material tion of
world, some are in motion and some are,
or appear to be, at rest. Of the bodies in
motion, some, like the sun and stars, ex-
hibit a constant movement, regular in
amount and direction, for which no ex-
ternal cause appears. Others, as stones
and smoke, seem also to move of them-
selves when external impediments are
taken away. But these appear to tend
to move in opposite directions : the bodies
we call heavy, such as stones, downwards,
and the bodies we call light, at least such

64 THE ADVANCE OF SCIENCE

as smoke and steam, upwards. And, as
we further notice that the earth, below
our feet, is made up of heavy matter,
while the air, above our heads, is ex-
tremely light matter, it is easy to regard
this fact as evidence that the lower region
is the place to which heavy things tend
— their proper place, in short — while the
upper region is the proper place of light
things ; and to generalise the facts ob-
served by saying that bodies, which are
free to move, tend towards their proper
places. All these seem to be natural mo-
tions, dependent on the inherent facul-
ties, or tendencies, of bodies themselves.
But there are other motions which are
artificial or violent, as when a stone is
thrown from the hand, or is knocked by
another stone in motion. In such cases
as these, for example, when a stone is
cast from the hand, the distance travelled
by the stone appears to depend partly on
its weight and partly upon the exertion

IN THE LAST HALF-CENTURY. 65

of the thrower. So that, the weight of
the stone remaining the same, it looks as
if the motive power communicated to it
were measured by the distance to which
the stone travels — as if, in other words,
the power needed to send it a hundred
yards was twice as great as that needed
to send it fifty yards. These, apparently
obvious, conclusions from the everyday
appearances of rest and motion fairly
represent the state of opinion upon the
subject which prevailed among the an-
cient Greeks, and remained dominant
until the age of Galileo. The publica-
tion of the ' Principia ' of Newton, in
1686-7, marks the epoch at which the
progress of mechanical physics had ef-
fected a complete revolution of thought
on these subjects. By this time, it had
been made clear that the old generalisa-
tions were either incomplete or totally
erroneous; that a body, once set in mo-
tion, will continue to move in a straight

66 THE ADVANCE OF SCIENCE

line for any conceivable time or distance,
unless it is interfered with ; that any
change of motion is proportional to the
'force' which causes it, and takes place
in the direction in which that 'force' is
exerted ; and that, w T hen a body in mo-
tion acts as a cause of motion on another,
the latter gains as much as the former
loses, and vice versa. It is to be noted,
however, that while, in contradistinction
to the ancient idea of the inherent tend-
ency to motion of bodies, the absence of
any such spontaneous power of motion
was accepted as a physical axiom by the
moderns, the old conception virtually
maintained itself in a new shape. For,
in spite of Newton's well-known warning
against the ' absurdity ' of supposing that
one body can act on another at a distance
through a vacuum, the ultimate particles
of matter were generally assumed to be
the seats of perennial causes of motion
termed 'attractive and repulsive forces,'

IN" THE LAST HALF-CENTUEY. 67

in virtue of which, any two such parti-
cles, without any external impression of
motion, or intermediate material agent,
were supposed to tend to approach or re-
move from one another ; and this view of
the duality of the causes of motion is
very widely held at the present day.

Another important result of investiga-
tion, attained in the seventeenth century,
was the proof and quantitative estimation
of physical inertia. In the old philoso-
phy, a curious conjunction of ethical and
physical prejudices had led to the notion
that there was something ethically bad
and physically obstructive about matter.
Aristotle attributes all irregularities and
apparent dysteleologies in nature to the
disobedience, or sluggish yielding, of mat-
ter to the shaping and guiding influence
of those reasons and causes which were
hypostatised in his ideal 'Forms.' In
modern science, the conception of the
inertia, or resistance to change, of matter

68 THE ADVANCE OF SCIENCE

is complex. In part, it contains a corol-
lary from the law of causation : A body
cannot change its state in respect of rest
or motion without a sufficient cause. But,
in part, it contains generalisations from
experience. One of these is that there is
no such sufficient cause resident in any
body, and that therefore it will rest, or
continue in motion, so long as no external
cause of change acts upon it. The other
is that the effect which the impact of a
body in motion produces upon the body
on which it impinges depends, other things
being alike, on the relation of a certain
quality of each which is called 'mass.'
Given a cause of motion of a certain value,
the amount of motion, measured by dis-
tance travelled in a certain time, which it
will produce in a given quantity of matter,
say a cubic inch, is not always the same,
but depends on what that matter is — a
cubic inch of iron will go faster than a
cubic inch of gold. Hence, it appears,

m THE LAST HALF-CENTUEY. 69

that since equal amounts of motion have,
ex hypothesi, been produced, the amount
of motion in a body does not depend on
its speed alone, but on some property of
tiie body. To this the name of 'mass'
has been given. And since it seems rea-
sonable to suppose that a large quantity
of matter, moving slowly, possesses as
much motion as a small quantity moving
faster, 'mass' has been held to express
'quantity of matter.' It is further de-
monstrable that, at any given time and
place, the relative mass of any two bod-
ies is expressed by the ratio of their
weights.

When all these great truths respecting
molar motion, or the movements of visible
and tangible masses, had been shown to
hold good not only of terrestrial bodies,
but of all those which constitute the visi-
ble universe, and the movements of the
macrocosm had thus been expressed by a
general mechanical theory, there remained

70 THE ADVANCE OF SCIENCE

a vast number of phenomena, such as
those of light, heat, electricity, magnet-
ism, and those of the physical and chemi-
cal changes, which do not involve molar
motion. Newton's corpuscular theory of
light was an attempt to deal with one
great series of these phenomena on me-
chanical principles, and it maintained its
ground until, at the beginning of the
nineteenth century, the undulatory theory
proved itself to be a much better working
hypothesis. Heat, up to that time, and
indeed much later, was regarded as an im-
ponderable substance, caloric ; as a thing
which was absorbed by bodies when they
were warmed, and was given out as they
cooled ; and which, moreover, was capable
of entering into a sort of chemical combi-
nation with them, and so becoming latent.
Rumford and Davy had given a great
blow to this view of heat by proving that
the quantity of heat which two portions
of the same body could be made to give

IN THE LAST HALF-CENTUKY. 71

out, by rubbing them together, was practi-
cally illimitable. This result brought phi-
losophers face to face with the contradic-
tion of supposing that a finite body could
contain an infinite quantity of another
body ; but it was not until 1843, that Mechan-
clear and unquestionable experimental ry of
proof was given of the fact that there is a ea "
definite relation between mechanical work
and heat ; that so much work always
gives rise, under the same conditions, to
so much heat, and so much heat to so
much mechanical work. Thus originated
the mechanical theory of heat, which be-
came the starting-point of the modern
doctrine of the conservation of energy.
Molar motion had appeared to be de-
stroyed by friction. It was proved that
no destruction took place, but that an
exact equivalent of the energy of the lost
molar motion appears as that of the mo-
lecular motion, or motion of the smallest
particles of a bodv, which constitutes

72 THE ADVANCE OF SCIENCE

heat. The loss of the masses is the gain
of their particles.
Earlier Before 1843, however, the doctrine of

proachcs ^ ne conservation of energy had been ap-
doctrine P roacne <i- Bacon's chief contribution to
of con- positive science is the happy guess (for
tion. the context shows that it was little more)
that heat may be a mode of motion ; Des-
cartes affirmed the quantity of motion in
the world to be constant ; Newton nearly
gave expression to the complete theorem ;
while Rumford's and Davy's experiments
suggested, though they did not prove,
the equivalency of mechanical and ther-
mal energy. Again, the discovery of vol-
taic electricity, and the marvellous de-
velopment of knowledge, in that field,
effected by such men as Davy, Fara-
day, Oersted, Ampere, and Melloni, had
brought to light a number of facts which
tended to show that the so-called ' forces '
at work in light, heat, electricity, and
magnetism, in chemical and in mechani-

IX THE LAST HALF- CENTURY. 73

cal operations, were intimately, and, in
various cases, quantitatively related. It
was demonstrated that any one could be
obtained at the expense of any other;
and apparatus was devised which exhib-
ited the evolution of all these kinds of
action from one source of energy. Hence
the idea of the 'correlation of forces'
which was the immediate forerunner of the
doctrine of the conservation of energy.

It is a remarkable evidence of the
greatness of the progress in this direction
which has been effected in our time, that
even the second edition of the 'History
of the Inductive Sciences,' which was
published in 1846, contains no allusion
either to the general view of the ' Corre-
lation of Forces ' published in England in
1842, or to the publication in 1843 of the
first of the series of experiments by which
the mechanical equivalent of heat was
correctly ascertained. * Such a failure on

* This is the more curious, as Ampere's hypothesis

74

THE ADVANCE OF SCIENCE

the part of a contemporary, of great ac-
quirements and remarkable intellectual
powers, to read the signs of the times, is
a lesson and a warning worthy of being
deeply pondered by anyone who attempts
to prognosticate the course of scientific
progress.

I have pointed out that the growth of
clear and definite views respecting the
constitution of matter has led to the con-
clusion that, so far as natural agencies

that vibrations of molecule?, causing and caused by vi-
brations of the ether, constitute heat, is discussed. See
vol. ii. p. 587, 2nd ed. In the Philosophy of, the In-
ductive Sciences, 2nd ed., 1847, p. 239, Whewell re-
marks, a propos of Bacon's definition of heat, ' that it is
an expansive, restrained motion, modified in certain
ways, and exerted in the smaller particles of the body ; '
that ' although the exact nature of heat is still an ob-
scure and controverted matter, the science of heat
now consists of many important truths ; and that to
none of these truths is there any approximation in
Bacon's essay.' In point of fact, Bacon's statement,
however much open to criticism, does contain a dis-
tinct approximation to the most important of all the
truths respecting heat which had been discovered when
Whewell wrote.

IN THE LAST HALF-CENTURY. 75

are concerned, it is ingenerable and inde-
structible. In so far as matter may be
conceived to exist in a purely passive
state, it is, imaginably, older than mo-
tion. But, as it must be assumed to be
susceptible of motion, a particle of bare
matter at rest must be endowed with the
potentiality of motion. Such a particle,
however, by the supposition, can have
no energy, for there is no cause why it
should move. Suppose now that it re-
ceives an impulse, it will begin to move
with a velocity inversely proportional to
its mass, on the one hand, and directly
proportional to the strength of the im-
pulse, on the other, and will possess ki-
netic energy, in virtue of which it will
not only continue to move for ever if un-
impeded, but if it impinges on another
such particle, it will impart more or less
of its motion to the latter. Let it be con-
ceived that the particle acquires a tenden-
cy to move, and that nevertheless it does

76 THE ADVANCE OF SCIENCE

not move. It is then in a condition total-
ly different from that in which it was at
first. A cause competent to produce mo-
tion is operating upon it, but, for some
reason or other, is unable to give rise to
motion. If the obstacle is removed, the
energy which was there, but could not
manifest itself, at once gives rise to mo-
tion. While the restraint lasts, the en-
ergy of the particle is merely potential ;
and the case supposed illustrates what is
meant by potential energy. In this con-
trast of the potential with the actual,
modern physics is turning to account the
most familiar of Aristotelian distinctions
— that between Suva/its and evepyeia.

That kinetic energy appears to be im-
parted by impact is a fact of daily and
hourly experience : we see bodies set in
motion by bodies, already in motion,
which seem to come in contact with them.
It is a truth which could have been learned
by nothing but experience, and which

IX THE LAST HALF-CENTURY. 77

cannot be explained, bnt must be taken
as an ultimate fact about which, explica-
ble or inexplicable, there can be no doubt.
Strictly speaking, we have no direct ap-
prehension of any other cause of motion.
But experience furnishes innumerable ex-
amples of the production of kinetic energy
in a body previously at rest, when no im-
pact is discernible as the cause of that en-
ergy. In all such cases, the presence of a
second body is a necessary condition ; and
the amount of kinetic energy, which its
presence enables the first to gain, is strict-
ly dependent on the relative positions of
the two. Hence the phrase energy of po-
sition, which is frequently used as equiva-
lent to potential energy. If a stone is
picked up and held, say, six feet above
the ground, it has potential energy, be-
cause, if let go, it will immediately begin
to move towards the earth ; and this en-
ergy may be said to be energy of position,
because it depends upon the relative posi-

78 THE ADVANCE OF SCIENCE

tion of the earth and the stone. The
stone is solicited to move but cannot, so
long as the muscular strength of the hold-
er prevents the solicitation from taking
effect. The stone, therefore, has potential
energy, which becomes kinetic if it is let
go, and the amount of that kinetic energy
which will be developed before it strikes
the earth depends on its position — on the
fact that it is, say, six feet off the earth,
neither more nor less. Moreover, it can
be proved that the raiser of the stone had
to exert as much energy in order to place
it in its position, as it will develop in fall-
ing. Hence the energy which was exert-
ed, and apparently exhausted, in raising
the stone, is potentially in the stone, in
its raised position, and will manifest itself
when the stone is set free. Thus the en-
ergy, withdrawn from the general stock
to raise the stone, is returned when it
falls, and there is no change in the total
amount. Energy, as a whole, is conserved.

IX THE LAST HALF-CEXTUEY. 79

Taking this as a very broad and gen-
eral statement of the essential facts of the
case, the raising of the stone is intelligible
enough, as a case of the communication
of motion from one body to another. But
the potential energy of the raised stone
is not so easily intelligible. To all ap-
pearance, there is nothing either pushing
or pulling it towards the earth, or the
earth towards it ; and yet it is quite cer-
tain that the stone tends to move towards
the earth and the earth towards the stone,
in the way defined by the law of gravita-
tion.

In the currently accepted language of
science, the cause of motion, in all such
cases as this, when bodies tend to move
towards or away from one or another,
without any discernible impact of other
bodies, is termed a 'force,' which is called
'attractive' in the one case, and 'repul-
sive' in the other. And such attractive
or repulsive forces are often spoken of as

80 THE ADVANCE OF SCIENCE

if they were real things, capable of exert-
ing a pull, or a push, npon the particles
of matter concerned. Thus the potential
energy of the stone is commonly said to
be due to the ' force ' of gravity which is
continually operating upon it.

Another illustration may make the case
plainer. The bob of a pendulum swings
first to one side and then to the other of
the centre of the arc which it describes.
Suppose it to have just reached the sum-
mit of its right-hand half-swing. It is
said that the 'attractive forces' of the
bob for the earth, and of the earth for the
bob, set the former in motion ; and as
these 'forces' are continually in opera-
tion, they confer an accelerated velocity
on the bob ; until, when it reaches the
centre of its swing, it is, so to speak, fully
charged with kinetic energy. If, at this
moment, the whole material universe, ex-
cept the bob, were abolished, it would
move for ever in the direction of a tangent

IN THE LAST HALF-CENTURY. 81

to the middle of the arc described. As a
matter of fact, it is compelled to travel
through its left-hand half -swing, and thus
virtually to go up hill. Consequently,
the ' attractive forces ' of the bob and the
earth are now acting against it, and con-
stitute a resistance which the charge of
kinetic energy has to overcome. But, as
this charge represents the operation of
the attractive forces during the passage of
the bob through the right-hand half-swing
down to the centre of the arc, so it must
needs be used up by the passage of the
bob upwards from the centre of the arc to
the summit of the left-hand half-swing.
Hence, at this point, the bob comes to a
momentary rest. The last fraction of
kinetic energy is just neutralised by the
action of the attractive forces, and the
bob has only potential energy equal to
that with which it started. So that the
sum of the phenomena may be stated

thus : At the summit of either half-arc of
6

82 THE ADVANCE OF SCIENCE

its swing, the bob has a certain amount of
potential energy ; as it descends it gradu-
ally exchanges this for kinetic energy,
until at the centre it possesses an equiva-
lent amount of kinetic energy ; from this
point onwards, it gradually loses kinetic
energy as it ascends, until, at the summit
of the other half-arc, it has acquired an
exactly similar amount of potential en-
ergy. Thus, on the whole transaction,
nothing is either lost or gained ; the quan-
tity of energy is always the same, but it
passes from one form into the other.

To all appearance, the phenomena ex-
hibited by the pendulum are not to be
accounted for by impact : in fact, it is
usually assumed that corresponding phe-
nomena would take place if the earth and
the rjendulum were situated in an abso-
lute vacuum, and at any conceivable dis-
tance from one another. If this be so, it
follows that there must be two totally dif-
ferent kinds of causes of motion : the one

IN THE LAST HALF- CENTURY. 83

impact— a vera causa, of which, to all ap-
pearance, we have constant experience ;
the other, attractive or repulsive 'force'
—a metaphysical entity which is physi-
cally inconceivable. Newton expressly
repudiated the notion of the existence of
attractive forces, in the sense in which
that term is ordinarily understood; and
he refused to put forward any hypothesis
as to the physical cause of the so-called
' attraction of gravitation.' As a general
rule, his successors have been content to
accept the doctrine of attractive and re-
pulsive forces, without troubling them-
selves about the philosophical difficulties
which it involves. But this has not al-
ways been the case ; and the attempt of
Le Sage, in the last century, to show that
the phenomena of attraction and repul-
sion are susceptible of explanation by his
hypothesis of bombardment by ultra-mun-
dane particles, whether tenable or not,
has the great merit of being an attempt

84 THE ADVANCE OF SCIENCE

to get rid of the dual conception of the
causes of motion which has hitherto pre-
vailed. On this hypothesis, the hammer-
ing of the ultra-mundane corpuscles on
the bob confers its kinetic energy, on the
one hand, and takes it away on the other ;
and the state of potential energy means
the condition of the bob during the instant
at which the energy, conferred by the ham-
mering during the one half -arc, has just
been exhausted by the hammering during
the other half -arc. It seems safe to look
forward to the time when the conception
of attractive and repulsive forces, having
served its purpose as a useful piece of
scientific scaffolding, will be replaced by
the deduction of the phenomena known
as attraction and repulsion, from the
general laws of motion.

The doctrine of the conservation of en-
ergy which I have endeavored to illustrate
is thus defined by the late Clerk Max-
well :

EST THE LAST HALF- CENTURY. 85

' The total energy of any body or sys-
tem of bodies is a quantity which can
neither be increased nor diminished by
any mutual action of such bodies, though
it may be transformed into any one of the
forms of which energy is susceptible.' It
follows that energy, like matter, is inde-
structible and ingenerable in nature. The
phenomenal world, so far as it is material,
expresses the evolution and involution of
energy, its passage from the kinetic to
the potential condition and back again.
Wherever motion of matter takes place,
that motion is effected at the expense of
part of the total store of energy.

Hence, as the phenomena exhibited by
living beings, in so far as they are mate-
rial, are all molar or molecular motions,
these are included under the general law.
A living body is a machine by which en-
ergy is transformed in the same sense as a
steam-engine is so, and all its movements,
molar and molecular, are to be accounted

86 THE ADVANCE OF SCIENCE

for by the energy which is supplied to it.
The phenomena of consciousness which
arise, along with, certain transformations
of energy, cannot be interpolated in the
series of these transformations, inasmuch
as they are not motions to which the doc-
trine of the conservation of energy ap-
plies. And, for the same reason, they do
not necessitate the using up of energy ;
a sensation has no mass and cannot be
conceived to be susceptible of movement.
That a particular molecular motion does
give rise to a state of consciousness is
experimentally certain ; but the how and
why of the process are just as inexpli-
cable as in the case of the communication
of kinetic energy by impact.

When dealing with the doctrine of the
ultimate constitution of matter, we found
a certain resemblance betweeen the oldest
speculations and the newest doctrines of
j)hysical philosophers. But there is no
such resemblance between the ancient and

IN THE LAST HALF-CENTURY.

87

modern views of motion and its causes,
except in so far as the conception of at-
tractive and repulsive forces may be re-
garded as the modified descendant of the
Aristotelian conception of forms. In fact,
it is hardly too much to say that the
essential and fundamental difference be-
tween ancient and modern physical sci-
ence lies in the ascertainment of the true
laws of statics and dynamics in the course
of the last three centuries ; and in the in-
vention of mathematical methods of deal-
ing with all the consequences of these
laws. The ultimate aim of modern physical
science is the deduction of the phenome-
na exhibited by material bodies from phy-
sico-mathematical first principles. Wheth-
er the human intellect is strong enough
to attain the goal set before it may be a
question, but thither will it surely strive.

The third great scientific event of our (3) Evo-
time, the rehabilitation of the doctrine of

88 THE ADVANCE OF SCIENCE.

evolution, is part of the same tendency
of increasing knowledge to unify itself,
which has led to the doctrine of the con-
servation of energy. And this tendency,
again, is mainly a product of the in-
creasing strength conferred by physical
investigation on the belief in the univer-
sal validity of that orderly relation of
facts, which we express by the so-called
' Laws of Nature.'

The growth of a plant from its seed, of
an animal from its egg, the apparent ori-
gin of innumerable living things from
mud, or from the putrefying remains of
former organisms, had furnished the ear-
lier scientific thinkers with abundant anal-
ogies suggestive of the conception of a
corresponding method of cosmic evolu-
tion from a formless ' chaos ' to an ordered
world which might either continue for ever
Early or undergo dissolution into its elements
oltSs before starting on a new course of evolu-
theory. t j on _ jj. j s therefore no wonder that.

IK THE LAST HALF-CENTUEY. 89

from the days of the Ionian school on-
wards, the view that the universe was the
result of such a process should have
maintaiued itself as a leading dogma
of philosophy. The emanistic theories
which played so great a part in Neopla-
tonic philosophy and Gfnostic theology are
forms of evolution. In the seventeenth
century, Descartes propounded a scheme
of evolution, as an hypothesis of what
might have been the mode of origin of the
world, while professing to accept the ec-
clesiastical scheme of creation, as an ac-
count of that which actually was its man-
ner of coming into existence. In the
eighteenth century, Kant put forth a re-
markable speculation as to the origin of
the solar system, closely similar to that
subsequently adopted by Laplace and
destined to become famous under the title
of the 'nebular hypothesis.'

The careful observations and the acute
reasonings of the Italian geologists of the

90 THE ADVANCE OF SCIENCE

seventeenth and eighteenth centuries ;
the speculations of Leibnitz in the 'Pro-
togsea ' and of Buffon in liis ' Theorie de
la Terre ; ' the sober and profound reason-
ings of Hutton, in the latter part of the
eighteenth century ; all these tended to
show that the fabric of the earth itself
implied the continuance of processes of
natural causation for a period of time as
great, in relation to human history, as the
distances of the heavenly bodies from us
are, in relation to terrestrial standards of
measurement. The abyss of time began
to loom as large as the abyss of space.
And this revelation to sight and touch, of
a link here and a link there of a practi-
cally infinite chain of natural causes and
effects, prepared the way, as perhaps
nothing else has done, for the modern
form of the ancient theory of evolution.
In the beginning of the eighteenth
century, De Maj IIeL. made the first seri-
ous attempt to apply the doctrine to the

IN THE LAST HALF-CENTUBY. 91

living world. In the latter part of it,
Erasmus Darwin, Goethe, Treviranus, and
L amar ck took up the work more vigor-
ously and with better qualifications. The
question of special creation, or evolution,
lay at the bottom of the fierce disputes
which broke out in the French Academy
between Cuvier and St.-Hilaire ; and, for
a time, the supporters of biological evolu-
tion were silenced, if not answered, by
the alliance of the greatest naturalist of
the age with their ecclesiastical oppo-
nents. Ca^astrorjhism, a short-sighted
teleology, and a still more short-sighted
orthodoxy, joined forces to crush evolu-
tion.

Lyell and Poulett Scrope, in this
country, resumed the work of the Italians
and of Hutton ; and the former, aided by
a marvellous power of clear exposition,
placed upon an irrefragable basis the
truth that natural causes are competent
to account for all events, which can be

92 THE ADVANCE OF SCIENCE

proved to have occurred, in the course of
the secular changes which have taken
place during the deposition of the strati-
fied rocks. The publication of ' The Prin-
ciples of Geology,' in 1830, constituted
an epoch in geological science. But it
also constituted an epoch in the modern
history of the doctrines of evolution, by
raising in the mind of every intelligent
reader this question : If natural causation
is competent to account for the not-living
part of our globe, why should it not ac-
count for the living part?

By keeping this question before the
public for some thirty years, Lyell,
though the keenest and most formidable
of the opponents of the transmutation
theory, as it was formulated by Lamarck,
was of the greatest possible service in
facilitating the reception of the sounder
doctrines of a later day. And, in like
fashion, another vehement opponent of
the transmutation of species, the elder

IS THE LAST HALF-CENTURY. 93

Agassiz, was doomed to help the cause he
hated. Agassiz not only maintained the
fact of the progressive advance in organi-
sation of the inhabitants of the earth at
each successive geological epoch, but he
insisted upon the analogy of the steps of
this progression with those by which the
embryo advances to the adult condition,
among the highest forms of each group.
In fact, in endeavoring to support these
views he went a good way beyond the
limits of any cautious interpretation of
the facts then known.

Although little acquainted with bio-
logical science, Whewell seems to have
taken particular pains with that part of
his work which deals with the history of
geological and biological speculation ; and
several chapters of his seventeenth and
eighteenth books, which comprise the his-
tory of physiology, of comparative anat-
omy and of the palsetiological sciences,
vividly reproduce the controversies of the

94 THE ADVANCE OF SCIEXCE

early days of the Victorian epoch. But
here, as in the case of the doctrine of the
conservation of energy, the historian of
the inductive sciences has no prophetic
insight ; not even a suspicion of that
which the near future was to bring forth.
And those who still repeat the once favor-
Darwin ite objection that Darwin's 'Origin of
Species ' is nothing but a new version of
the 'Philosophic zoologique' will find
that, so late as 1844, Whewell had not
the slightest suspicion of Darwin's main
theorem, even as a logical possibility. In
fact, the publication of that theorem by
Darwin and Wallace, in 1859, took all
the biological world by surprise. Neither
those who were inclined towards the
' progressive transmutation' or 'develop-
ment ' doctrine, as it was then called, nor
those who were opposed to it, had the
slightest suspicion that the tendency to
variation in living beings, which all ad-
mitted as a matter of fact ; the selective

IX THE LAST HALF- CENTURY. 95

influence of conditions, which no one
could deny to be a matter of fact, when
his attention was drawn to the evidence ;
and 'me occurrence of great geological
changes which also was matter of fact ;
could be used as the only necessary pos-
tulates of a theory of the evolution of
plants and animals which, even if not, at
once, competent to explain all the known
facts of biological science, could not be
shown to be inconsistent with any. So
far as biology is concerned, the publica-
tion of the 'Origin of Species,' for the
first time, put the doctrine of evolution,
in its application to living things, upon a
sound scientific foundation. It became
an instrument of investigation, and in no
hands did it prove more brilliantly profit-
able than in those of Darwin himself.
His publications on the effects of domesti-
cation in plants and animals, on the influ-
ence of cross-fertilisation, on flowers as
organs for effecting such fertilisation, on

96 THE ADVANCE OF SCIENCE

insectivorous plants, on the motions of
plants, pointed out the routes of explora-
tion which have since been followed by
hosts of inquirers, to the great profit of
science.

Darwin found the biological world a
more than sufficient field for even his
great powers, and left the cosmical part
of the doctrine to others. ]S~ot much has
been added to the nebular hypothesis,
since the time of Laplace, except that the
attempt to show (against that hypothesis)
that all nebula? are star clusters, has been
met by the spectroscopic proof of the
gaseous condition of some of them. More-
over, physicists of the present generation
appear now to accept the secular cooling
of the earth, which is one of the corol-
laries of that hypothesis. In fact, at-
tempts have been made, by the help of
deductions from the data of physics, to
lay down an approximate limit to the
number of millions of years which have

IN THE LAST HALF-CENTTJRY. 97

elapsed since the earth was habitable by
living beings. If the conclusions thus
reached should stand the test of further
investigation, they will undoubtedly be
very valuable. But, whether true or
false, they can have no influence upon
the doctrine of evolution in its applica-
tion to living organisms. The occurrence
of successive forms of life upon our globe
is an historical fact, which cannot be dis-
puted ; and the relation of these success-
ive forms, as stages of evolution of the
same type, is established in various cases.
The biologist has no means of determin-
ing the time over which the process of
evolution has extended, but accepts the
computation of the physical geologist
and the physicist, whatever that may be.

Evolution as a philosophical doctrine and phi-
losophy,
applicable to all phenomena, whether

physical or mental, whether manifested

by material atoms or by men in society,

has been dealt with systematically in the

98 THE ADVANCE OF SCIENCE

'Synthetic Philosophy ' of Mr. Herbert
Spencer. Comment on that great under-
taking would not be in place here. I
mention it because, so far as I know, it is
the first attempt to deal, on scientific prin-
ciples, with modern scientific facts and
speculations. For the ' Philosophie posi-
tive' of M. Comte, with which Mr. Spen-
cer's system of philosophy is sometimes
compared, though it professes a similar
object, is unfortunately permeated by a
thoroughly unscientific spirit, and its au-
thor had no adequate acquaintance with
the physical sciences even of his own time.

The doctrine of evolution, so far as the
present physical cosmos is concerned, pos-
tulates the fixity of the rules of operation
of the causes of motion in the material
universe. If all kinds of matter are modi-
fications of one kind, and if all modes of
motion are derived from the same energy,
the orderly evolution of physical nature

I?* THE LAST HALF-CENTURY. 99

out of one substratum and one energy im-
plies that the rules of action of that energy
should be fixed and definite. In the past
history of the universe, back to that point,
there can be no room for chance or dis-
order. But it is possible to raise the ques-
tion whether this universe of simplest
matter and definitely operating energy,
which forms our hypothetical starting
point, may not itself be a product of evo-
lution from a universe of such matter, in
which the manifestations of energy were
not definite— in which, for example, our
laws of motion held good for some units
and not for others, or for the same units
at one time and not at another — and
which would therefore be a real epicurean
chance-world ?

For myself, I must confess that I find
the air of this region of speculation too
rarefied for my constitution, and I am dis-
posed to take refuge in 'ignoramus et
ignorabimus.'

100 THE ADVANCE OF SCIENCE

other The execution of my further task, the

ticliicvG"

merits in indication of the most important achieve-
science! 1 ments i n tne several branches of physical
science during the last fifty years, is em-
barrassed by the abundance of the objects
of choice ; and by the difficulty which
everyone, but a specialist in each depart-
ment, must find in drawing a due distinc-
tion between discoveries which strike the
imagination by their novelty, or by their
practical influence, and those unobtrusive
but pregnant observations and experi-
ments in which the germs of the great
things of the future really lie. Moreover,
my limits restrict me to little more than a
bare chronicle of the events which I have
to notice.
Physics In physics and chemistry, the old

chemis- boundaries of which sciences are rapidly
trjr - becoming effaced, one can hardly go wrong
in ascribing a primary value to the inves-
tigations into the relation between the
solid, liquid, and gaseous states of matter

IX THE LAST HALF-CENTURY. 101

on the one hand, and degrees of pressure
and of heat on the other. Almost all,
even the most refractory, solids have been
vaporised by the intense heat of the elec-
tric arc ; and the most refractory gases
have been forced to assume the liquid,
and even the solid, forms by the combina-
tion of high pressure with intense cold.
It has further been shown that there is no
discontinuity between these states — that a
gas passes into the liquid state through a
condition which is neither one nor the
other, and that a liquid body becomes
solid, or a solid liquid, by the intermedia-
tion of a condition in which it is neither
truly solid nor truly liquid.

Theoretical and experimental investi-
gations have concurred in the establish-
ment of the view that a gas is a body, the
particles of which are in incessant recti-
linear motion at high velocities, colliding
with one another and bounding back when
they strike the walls of the containing

102 THE ADVANCE OF SCIENCE

vessel; and, on this theory, the already
ascertained relations of gaseons bodies to
heat and pressure have been shown to
be deducible from mechanical principles.
Immense improvements have been effected
in the means of exhausting a given space
of its gaseous contents ; and experimenta-
tion on the phenomena which attend the
electric discharge and the action of ra-
diant heat, within the extremely rarefied
media thus produced, has yielded a great
number of remarkable results, some of
which have been made familiar to the
public by the Gieseler tubes and the ra-
diometer. Already, these investigations
have afforded an unexpected insight into
the constitution of matter and its rela-
tions with thermal and electric energy,
and they open up a vast field for future
inquiry into some of the deepest problems
of physics. Other important steps, in the
same direction, have been effected by in-
vestigations into the absorption of radiant

IN THE LAST HALF-CENTURY. 103

heat proceeding from different sources by
solid, fluid, and gaseous bodies. And it
is a curious example of the interconnec-
tion of the various branches of physical
science, that some of the results thus ob-
tained have proved of great importance in
meteorology.

The existence of numerous dark lines,
constant in their number and position in
the various regions of the solar spectrum,
was made out by Fraunhofer in the early
part of the present century, but more than
forty years elapsed before their causes
were ascertained and their importance rec-
ognised. Spectroscopy, which then took
its rise, is probably that employment of
physical knowledge, already won, as a
means of further acquisition, which most
impresses the imagination. For it has The
suddenly and immensely enlarged our scope!°"
power of overcoming the obstacles which
almost infinite minuteness on the one
hand, and almost infinite distance on the

104 THE ADVANCE OF SCIENCE

other, have hitherto opposed to the recog-
nition of the presence and the condition
of matter. One eighteen-millionth of a
grain of sodinm in the flame of a spirit-
lamp may be detected by this instrument ;
and, at the same time, it gives trust-
worthy indications of the material consti-
tution not only of the sun, but of the
farthest of those fixed stars and nebulae
which afford sufficient light to affect the
eye, or the photographic plate, of the in-
quirer.
Elec- The mathematical and experimental

elucidation of the phenomena of electrici-
ty, and the study of the relations of this
form of energy with chemical and thermal
action, had made extensive progress be-
fore 1837. But the determination of the
influence of magnetism on light, the dis-
covery of diamagnetism, of the influence
of crystalline structure on magnetism, and
the completion of the mathematical theory
of electricity, all belong to the present

IX THE LAST HALF-CENTURY. 105

epoch. To it also appertain the practical
execution and the working out of the
results of the great international system
of observations on terrestrial magnetism,
suggested by Humboldt in 1836 ; and the
invention of instruments of infinite deli-
cacy and precision for the quantitative de-
termination of electrical phenomena. The
voltaic battery has received vast improve-
ments ; while the invention of magneto-
electric engines and of improved means of
producing ordinary electricity has pro-
vided sources of electrical energy vastly
superior to any before extant in power,
and far more convenient for use.

It is perhaps this branch of physical
science which may claim the palm for its
practical fruits, no less than for the aid
which it has furnished to the investigation
of other parts of the field of physical sci-
ence. The idea of the practicability of es-
tablishing a communication between dis-
tant points, by means of electricity, could

106 THE ADVANCE OF SCIENCE

hardly fail to have simmered in the minds
of ingenious men since, well nigh a cent-
ury ago, experimental proof was given
that electric disturbances could be propa-
gated through a wire twelve thousand feet
long. Various methods of carrying the
suggestion into practice had been carried
out with some degree of success ; but the
system of electric telegraphy, which, at
the present time, brings all parts of the
civilised world within a few minutes of
one another, originated only about the
commencement of the epoch under con-
^ sideration. In its influence on the course
J of human affairs, this invention takes its
place beside that of gunpowder, which
tended to abolish the physical inequalities
of fighting men ; of printing, which tended
to destroy the effect of inequalities in
wealth among learning men ; of steam
transport, which has done the like for
travelling men. All these gifts of science
are aids in the process of levelling up ; of

IN THE LAST HALF-CENTURY. 107

removing the ignorant and baneful preju-
dices of nation against nation, province
against province, and class against class ;
of assuring that social order which is the
foundation of progress, which has re-
deemed Europe from barbarism, and
against which one is glad to think that
those who, in our time, are employing
themselves in fanning the embers of an-
cient wrong, in setting class against class,
and in trying to tear asunder the existing
bonds of unity, are undertaking a futile
struggle. The telephone is only second
in practical importance to the electric tele-
graph. Invented, as it were, only the other
day, it has already taken its place as an
appliance of daily life. Sixty years ago, the
extraction of metals from their solutions,
by the electric current, was simply a high-
ly interesting scientific fact. At the pres-
ent day, the galvano-plastic art is a great
industry ; and, in combination with pho-
tography, promises to be of endless service

108 THE ADVANCE OF SCIENCE

in the arts. Electric lighting is another
great gift of science to civilisation, the
practical effects of which have not yet
been fully developed, largely on account
of its cost. But those whose memories
go back to the tinder-box period, and
recollect the cost of the first lucifer
matches, will not despair of the results of
the application of science and ingenuity
to the cheap production of anything for
which there is a large demand.

The influence of the progress of elec-
trical knowledge and invention upon that
of investigation in other fields of science
is highly remarkable. The combination
of electrical with mechanical contrivances
has produced instruments by which, not
only may extremely small intervals of
time be exactly measured, but the varying
rapidity of movements, which take place
in such intervals and appear to the or-
dinary sense instantaneous, is recorded.
The duration of the winking of an eye is

IX THE LAST HALF-CENTURY. 109

a proverbial expression for an instantane-
ous action ; but, by the help of the revolv-
ing cylinder and the electrical marking-
apparatus, it is possible to obtain a graphic
record of such an action, in which, if it
endures a second, that second shall be
subdivided into a hundred, or a thousand,
equal parts, and the state of the action at
each hundredth, or thousandth, of a sec-
ond exhibited. In fact, these instruments
may be said to be time-microscopes. Such
appliances have not only effected a revo-
lution in physiology, by the power of
analysing the phenomena of muscular and
nervous activity which they have con-
ferred, but they have furnished new
methods of measuring the rate of move-
ment of projectiles to the artillerist.
Again, the microphone, which renders the
minutest movements audible, and which
enables a listener to hear the footfall of a
fly, has equipped the sense of hearing
with the means of entering almost as deep-

science.

110 THE ADVANCE OP SCIENCE

ly into the penetralia of nature, as does
the sense of sight.
Photog- That light exerts a remarkable influ-
aKm 7 ence in bringing about certain chemical
men? of combinations and decompositions was well
known fifty years ago, and various more
or less successful attempts to produce
permanent pictures, by the help of that
knowledge, had already been made. It
was not till 1839, however, that practical
success was obtained ; but the ' daguerre-
otypes ' were both cumbrous and costly,
and photography would never have at-
tained its present important development
had not the progress of invention substi-
tuted paper and glass for the silvered
plates then in use. It is not my affair to
dwell upon the practical application of
the photography of the present day, but
it is germane to my purpose to remark
that it has furnished a most valuable ac-
cessory to the methods, of recording mo-
tions and lapse of time already in exist-

IN THE LAST HALF-CENTURY. Ill

ence. In the hands of the astronomer and
the meteorologist, it has yielded means
of registering terrestrial, solar, planetary,
and stellar phenomena, independent of
the sources of error attendant on ordinary
observation ; in the hands of the physi-
cist, not only does it record spectroscopic
phenomena with unsurpassable ease and
precision, but it has revealed the exist-
ence of rays having powerful chemical
energy, i&r beyond the visible limits of
either end of the spectrum ; while, to the
naturalist, it furnishes the means by
which the forms of many highly compli-
cated objects may be represented, without
that possibility of error which is inherent
in the work of the draughtsman. In fact,
iu many cases, the stern impartiality of
photography is an objection to its em-
ployment : it makes no distinction be-
tween the important and the unimpor-
tant ; and hence photographs of dissec-
tions, for example, are rarely so useful

omy,

112 THE ADVANCE OF SCIENCE

as the work of a draughtsman who is at
once accurate and intelligent.
Astron- The determination of the existence of

a new planet, Neptune, far beyond the
previously known bounds of the solar
system, by mathematical deduction from
the facts of perturbation ; and the immedi-
ate confirmation of that determination, in
the year 1846, by observers who turned
their telescopes into the part of the heav-
ens indicated as its place, constitute a re-
markable testimony of nature to the valid-
ity of the principles of the astronomy of
our time. In addition, so many new as-
teroids have been added to those which
were already known to circulate in the
place which theoretically should be occu-
pied by a planet, between Mars and Jupi-
ter, that their number now amounts to
between two and three hundred. I have
already alluded to the extension of our
knowledge of the nature of the heavenly
bodies by the employment of spectros-

IN THE LAST HALF-CENTURY. 113

copy. It has not only thrown wonder-
ful light upon the physical and chemical
constitution of the sun, fixed stars, and
nebulae, and comets, but it holds out a
prospect of obtaining definite evidence
as to the nature of our so-called element-
ary bodies.

The application of the generalisations its rela-
of thermotics to the problem of the dura- geology.
tion of the earth, and of deductions from
tidal phenomena to the determination of
the length of the day and of the time of
revolution of the moon, in past epochs of
the history of the universe ; and the dem-
onstration of the competency of the great
secular changes, known under the general
name of the precession of the equinoxes,
to cause corresponding modifications in
the climate of the two hemispheres of our
globe, have brought astronomy into inti-
mate relation with geology. Geology, in
fact, proves that, in the course of the past
history of the earth, the climatic condi-

114 THE ADVANCE OF SCIENCE

tions of the same region have been widely
different, and seeks the explanation of
this important truth from the sister sci-
ences. The facts that, in the middle of
the Tertiary epoch, evergreen trees
abounded within the arctic circle ; and
that, in the long subsequent Quaternary
epoch, an arctic climate, with its accom-
paniment of gigantic glaciers, obtained
in the northern hemisphere, as far south
as Switzerland and Central France, are
as well established as any truths of sci-
ence. But, whether the explanation of
these extreme variations in the mean tem-
perature of a great part of the northern
hemisphere is to be sought in the con-
comitant changes in the distribution of
land and water surfaces of which geology
afiH^ds evidence, or in astronomical con-
ditions, such as those to which I have
referred, is a question which must await
its answer from the science of the fu-
ture.

IN THE LAST HALF-CENTURY. 115

Turning now to the great steps in that Bio-

. logical

vast progress which the biological sciences sciences.
have made since 1837, we are met, on the
threshold of our epoch, with perhaps the
greatest of all — namely, the promulgation
by Schwann, in 1839, of the generalisa-
tion known as the ' cell theory,' the appli- K he ' ce , n
cation and extension of which by a host of
subsequent investigators has revolution-
ised morphology, development, and physi-
ology. Thanks to the immense series of
labors thus inaugurated, the following fun-
damental truths have been established.

All living bodies contain substances of Funda-

mental

closely similar physical and chemical com- truths
position, which constitute the physical lished.
basis of life, known as protoplasm. So
far as our present knowledge goes, this
takes its origin only from pre-existing
protoplasm.

All complex living bodies consist, at
one period of their existence, of an aggre-
gate of minute portions of such substance,

116 THE ADVANCE OF SCIENCE

of similar structure, called cells, each cell
having its own life independent of the
others, though influenced by them.

All the morphological characters of ani-
mals and plants are the results of the mode
of multiplication, growth, and structural
metamorphosis of these cells, considered
as morphological units.

All the physiological activities of ani-
mals and plants — assimilation, secretion,
excretion, motion, generation — are the ex-
pression of the activities of the cells con-
sidered as physiological units. Each in-
dividual, among the higher animals and
plants, is a synthesis of millions of subor-
dinate individualities. Its individuality,
therefore, is that of a ' civitas ' in the
ancient sense, or that of the Leviathan of
Hobbes.

There is no absolute line of demarca-
tion between animals and plants. The
intimate structure, and the modes of
change, in the cells of the two are funda-

IN THE LAST IIALF-CENTUEY. 117

mentally the same. Moreover, the higher
forms are evolved from lower, in the
course of their development, by analogous
processes of differentiation, coalescence,
and reduction in both the vegetable and
the animal worlds.

At the present time, the cell theory, in
consequence of recent investigations into
the structure and metamorphosis of the
'nucleus,' is undergoing a new develop-
ment of great significance, which, among
other things, foreshadows the possibility
of the establishment of a physical theory
of heredity, on a safer foundation than
those which Buffon and Darwin have de-
vised.

The popular belief in abiogenesis, or Sponta-
the so-called ' spontaneous ' generation of genera-

r tion dis-

the lower forms of life, which was ac- proved,
cepted by all the philosophers of antiqui-
ty, held its ground down to the middle of
the seventeenth century. Notwithstand-
ing the frequent citation of the phrase,

118 THE ADVANCE OF SCIENCE

wrongfully attributed to Harvey, 'Omne
vivum ex ovo,' that great physiologist be-
lieved in spontaneous generation as firmly
as Aristotle did. And it was only in the
latter part of the seventeenth century,
that Redi, by simple and well-devised ex-
periments, demonstrated that, in a great
number of cases of supposed spontaneous
generation, the animals which made their
appearance owed their origin to the ordi-
nary process of reproduction, and thus
shook the ancient doctrine to its founda-
tions. In the middle of the eighteenth
century, it was revived, in a new form, by
Needham and Buffon ; but the experi-
ments of Spallanzani enforced the conclu-
sions of Redi, and compelled the advo-
cates of the occurrence of spontaneous
generation to seek evidence for their hy-
pothesis only among the parasites and the
lowest and minutest organisms. It is
just fifty years since Schwann and others
proved that, even with respect to them,

IN THE LAST HALF-CENTURY. 119

the supposed evidence of abiogenesis was
untrustworthy.

During the present epoch, the ques-
tion, whether living matter can be pro-
duced in any other way than by the phys-
iological activity of other living matter,
has been discussed afresh with great
vigor ; and the problem has been investi-
gated by experimental methods of a pre-
cision and refinement unknown to previ-
ous investigators. The result is that the
evidence in favor of abiogenesis has ut-
terly broken down, in every case which
has been properly tested. So far as the
lowest and minutest organisms are con-
cerned, it has been proved that they
never make their appearance, if those pre-
cautions by which their germs are cer-
tainly excluded are taken. And, in re-
gard to parasites, every case which seemed
to make for their generation from the
substance of the animal, or plant, which
they infest has been proved to have a to-

120 THE ADVANCE OF SCIENCE

tally different significance. Whether not-
living matter may pass, or ever has, un-
der any conditions, passed into living
matter, without the agency of pre-exist-
ing living matter, necessarily remains an
open question ; all that can be said is that
it does not undergo this metamorphosis
under any known conditions. Those who
take a monistic view of the physical
world may fairly hold abiogenesis as a
pious opinion, supported by analogy and
defended by our ignorance. But, as mat-
ters stand, it is equally justifiable to re-
gard the physical world as a sort of dual
monarchy. The kingdoms of living mat-
ter and of not-living matter are under one
system of laws, and there is a perfect
freedom of exchange and transit from one
to the other. But no claim to biological
nationality is valid except birth.
Mor- In the department of anatomy and de-

velopment, a host of accurate and patient
inquirers, aided by novel methods of

phology.

IN THE LAST HALF-CENTURY. 121

preparation, which enable the anatomist
to exhaust the details of visible structure
and to reproduce them with geometrical
precision, have investigated every impor-
tant group of living animals and plants, no
less than the fossil relics of former faunae
and flora?. An enormous addition has
thus been made to our knowledge, espe-
cially of the lower forms of life, and it
may be said that morphology, however
inexhaustible in detail, is complete in its
broad features. Classification, which is
merely a convenient summary expression
of morphological facts, has undergone a
corresponding improvement. The breaks
which formerly separated our groups from
one another, as animals from plants, ver-
tebrates from invertebrates, cryptogams
from phanerogams, have either been filled
up, or shown to have no theoretical sig-
nificance. The question of the position
of man, as an animal, has given rise to
much disputation, with the result of prov-

122 THE ADVANCE OF SCIENCE.

ing that there is no anatomical or develop-
mental character by which he is more
widely distinguished from the group of
animals most nearly allied to him, than
they are from one another. In fact, in
this particular, the classification of Lin-
nseus has been proved to be more in ac-
cordance with the facts than those of most
of his successors.
Anthro- The study of man, as a genus and
species of the animal world, conducted
with reference to no other considerations
than those which would be admitted by
the investigator of any other form of ani-
mal life, has given rise to a special branch
of biology, known as Anthropology,
which has grown with great rapidity.
Numerous societies devoted to this por-
tion of science have sprung up, and the
energy of its devotees has produced a co-
pious literature. The physical characters
of the various races of men have been
studied with a minuteness and accuracy

IX THE LAST HALF- CENTURY. 123

heretofore unknown ; and demonstrative
evidence of the existence of human con-
temporaries of the extinct animals of the
latest geological epoch has been obtained,
physical science has thus been brought
into the closest relation with history and
with archaeology ; and the striking inves-
tigations which, during our time, have
put beyond doubt the vast antiquity of
Babylonian and Egyptian civilisation, are
in perfect harmony with the conclusions
of anthropology as to the antiquity of
the human species.

Classification is a logical process which
consists in putting together those things
Avhich are like and keeping asunder those
which are unlike ; and a morphological
classification, of course, takes notes only
of morphological likeness and unlikeness.
So long, therefore, as our morphological
knowledge was almost wholly confined to
anatomy, the characters of groups were
solely anatomical ; but as the phenomena

124 THE ADVANCE OF SCIENCE

of embryology were explored, the like-
ness and nnlikeness of individual devel-
opment had to be taken into account ;
and, at present, the study of ancestral
evolution introduces a new element of
likeness and unlikeness which is not only
eminently deserving of recognition, but
must ultimately predominate over all oth-
ers. A classification which shall repre-
sent the process of ancestral evolution is,
in fact, the end which the labors of the
philosophical taxonomist must keep in
view. But it is an end which cannot be
attained until the progress of palaeontolo-
gy has given us far more insight than Ave
yet possess, into the historical facts of the
case. Much of the speculative ' phyloge-
ny," which abounds among my present
contemporaries, reminds me very forcibly
of the speculative morphology, unchecked
by a knowledge of development, which
was rife in my youth. As hypothesis,
suggesting inquiry in this or that direc-

EN THE LAST HALF-CEXTURY. 125

tion, it is often extremely useful ; but,
when the product of such speculation is
placed on a level with those generalisa-
tions of morphological truths which are
represented by the definitions of natural
groups, it tends to confuse fancy with
fact and to create mere confusion. We
are in danger of drifting into a new
' Natur-Philosophie ' worse than the old,
because there is less excuse for it. Boyle
did great service to science by his ' Scep-
tical Chemist,' and I am inclined to think
that, at the present day, a ' Sceptical
Biologist ' might exert an equally benefi-
cent influence.

"Whoso wishes to gain a clear concep- Physiol-
tion of the progress of physiology, since
1837, will do well to compare Muller's
'Physiology,' which appeared in 1835,
and Drapiez's edition of Richard's ' Nou-
veaux Elements de Botanique,' published
in 1S37, with any of the present hand-
books of animals and vegetable physiolo-

ogy-

126 THE ADVANCE OF SCIENCE

gy. Muller's work was a masterpiece, un-
surpassed since the time of Haller, and
Richard's book enjoyed a great reputation
at the time ; but their successors trans-
port one into a new world. That which
characterises the new physiology is that
it is permeated by, and indeed based ivp-
on, conceptions which, though not wholly
absent, are but dawning on the minds of
the older writers.

Modern physiology sets forth as its
chief ends : Firstly, the ascertainment of
the facts and conditions of cell-life in
general. Secondly, in composite organ-
isms, the analysis of the functions of
organs into those of the cells of which they
are composed. Thirdly, the explication
of the processes by which this local cell-
life is directly, or indirectly, controlled
and brought into relation with the life of
the rest of the cells which compose the
organism. Fourthly, the investigation of
the phenomena of life in general, on the

IN THE LAST HALF-CENTURY. 127

assumption that the physical and chemi-
cal processes which take place in the living
body are of the same order as those which
take place out of it ; and that whatever
energy is exerted in producing such phe-
nomena is derived from the common stock
of energy in the universe. In the fifth
place, modern physiology investigates the
relation between physical and psychical
phenomena, on the assumption that mo-
lecular changes in definite portions of
nervous matter stand in the relation of
necessary antecedents to definite mental
states and operations. The work which
has been done in each of the directions
here indicated is vast, and the accumula-
tion of solid knowledge, which has been
effected, is correspondingly great. For the
first time in the history of science, physi-
ologists are now in the position to say
that they have arrived at clear and dis-
tinct, though by no means complete, con-
ceptions of the manner in which the great

128 THE ADVANCE OF SCIENCE

functions of assimilation, respiration, se-
cretion, distribution of nutriment, removal
of waste products, motion, sensation, and
reproduction are performed ; while the
operation of the nervous system, as a
regulative apparatus, which influences the
origination and the transmission of mani-
festations of activity, either within itself
or in other organs, has been largely eluci-
dated.
Practi- I have pointed out, in an earlier part

cal value . . .

of physi- oi this chapter, that the history ot all
disfov- branches of science proves that they must
ery " attain a considerable stage of development
before they yield practical ' fruits ; ' and
this is eminently true of physiology. It
is only within the present epoch, that
physiology and chemistry have reached
the point at which they could offer a sci-
entific foundation to agriculture ; and it
is only within the present epoch, that
zoology and physiology have yielded any
very great aid to pathology and hygiene.

IN THE LAST HALF-CENTURY. 129

But within that time, they have already
rendered highly important services by the
exploration of the phenomena of parasi-
tism. Not only have the history of the
animal parasites, such as the tapeworms
and the trichina, which infest men and
animals, with deadly results, been cleared
up by means of experimental investiga-
tions, and efficient modes of prevention
deduced from the data so obtained ; but
the terrible agency of the parasitic fungi
and of the infinitesimally minute microbes,
which work far greater havoc among
plants and animals, has been brought to
light. The 'particulate' or 'germ' the-
ory of disease, as it is called, long since
suggested, has obtained a firm foundation,
in so far as it has been proved to be true
in respect of sundry epidemic disorders.
Moreover, it has theoretically justified pro-
phylactic measures, such as vaccination,
which formerly rested on a merely empiri-
cal basis ; and it has been extended to

9

130 THE ADVANCE OF SCIENCE

other diseases with excellent results. Fur-
ther, just as the discovery of the cause of
scabies proved the absurdity of many
of the old prescriptions for the preven-
tion and treatment of that disease ; so
the discovery of the cause of splenic fever,
and other such maladies, has given a new
direction to prophylactic and curative
measures against the worst scourges of hu-
manity. Unless the fanaticism of philo-
zoic sentiment overpowers the voice of
philanthropy, and the love of dogs and
cats supersedes that of one's neighbor, the
progress of experimental physiology and
pathology will, indubitably, in course of
time, place medicine and hygiene upon a
rational basis. Two centuries ago Eng-
land was devastated by the plague ; clean-
liness and common sense were enough to
free us from its ravages. One century
since, small-pox was almost as great a
scourge ; science, though working empiri-
cally, and almost in the dark, has reduced

IN THE LAST HALF-CENTURY. 131

that evil to relative insignificance. At the
present time, science, working in the light
of clear knowledge, has attacked splenic
fever and has beaten it ; it is attacking
hydrophobia with no mean promise of
success ; sooner or later it will deal, in
the same way, with diphtheria, typhoid
and scarlet fever. To one who has seen
half a street swept clear of its children,
or has lost his own by these horrible pes-
tilences, passing one's offspring through
the fire to Moloch seems humanity, com-
pared with the proposal to deprive them
of half their chances of health and life
because of the discomfort to dogs and
cats, rabbits and frogs, which may be in-
volved in the search for means of guard-
ing them.

An immense extension has been ef- Scienti-

fic C5plo-

fected in our knowledge of the distribu- ration.
tion of plants and animals ; and the eluci-
dation of the causes which have brought
about that distribution has been greatly

132 THE ADVANCE OF SCIENCE

advanced. The establishment of meteoro-
logical observations by all civilised na-
tions, has furnished a solid foundation to
climatology ; while a growing sense of the
importance of the influence of the ' strug-
gle for existence' affords a wholesome
check to the tendency to overrate the in-
fluence of climate on distribution. Ex-
peditions, such as that of the 'Chal-
lenger,' equipped, not for geographical
exploration and discovery, but for the
purpose of throwing light on problems of
physical and biological science, have been
sent out by our own and other Govern-
ments, and have obtained stores of in-
formation of the greatest value. For the
first time, we are in possession of some-
thing like precise knowledge of the physi-
cal features of the deep seas, and of the
living population of the floor of the ocean.
The careful and exhaustive study of the
phenomena presented by the accumula-
tions of snow and ice, in polar and mount-

IN THE LAST UALF-CEN'TURY. 133

ainous regions, which has taken place in
our time, has not only revealed to the
geologist an agent of denudation and
transport, which has slowly and quietly
produced effects, formerly confidently re-
ferred to diluvial catastrophes, but it has
suggested new methods of accounting for
various puzzling facts of distribution.

Palaeontology, which treats of the ex- Paiaeon-
tinct forms of life and their succession
and distribution upon our globe, a branch
of science which could hardly be said to
exist a century ago, has undergone a won-
derful development in our epoch. In
some groups of animals and plants, the
extinct representatives, already known,
are more numerous and important than
the living. There can be no doubt that
the existing Fauna and FJora is but the
last term of a long series of equally nu-
merous contemporary species, which have
succeeded one another, by the slow and
gradual substitution of species for species,

134 THE ADVANCE OF SCIENCE

in the vast interval of time which has
elapsed between the deposition of the
earliest fossiliferous strata and the pres-
ent day. There is no reasonable ground
for believing that the oldest remains yet
obtained carry ns even near the begin-
nings of life. The impressive warnings
of Lyell against hasty speculations, based
upon negative evidence, have been fully
justified ; time after time, highly organ-
ised types have been discovered in forma-
tions of an age in which the existence of
such forms of life had been confidently
declared to be impossible. The western
territories of the United States alone have
yielded a world of extinct animal forms,
undreamed of fifty years ago. And, wher-
ever sufficiently numerous series of the
remains of any given group, which has
endured for a long space of time, are
carefully examined, their morphological
relations are never in discordance with the
requirements of the doctrine of evolution,

IN THE LAST HALF- CENTURY. 135

and often afford convincing evidence of
it. At the same time, it has been shown
that certain forms persist with very little
change, from the oldest to the newest fos-
siliferons formations ; and thus show that
progressive development is a contingent,
and not a necessary result, of the nature
of living matter.

Geology is, as it were, the biology of Geology.
our planet as a whole. In so far as it
comprises the surface configuration and
the inner structure of the earth, it answers
to morphology ; in so far as it studies
changes of condition and their causes, it
corresponds with physiology ; in so far as
it deals with the causes which have effect-
ed the progress of the earth from its ear-
liest to its present state, it forms part
of the general doctrine of evolution. An
interesting contrast between the geology
of the present day and that of half a cent-
ury ago, is presented by the complete
emancipation of the modern geologist

138 THE ADVANCE OF SCIENCE

from the controlling and perverting influ-
ence of theology, all-powerful at the ear-
lier date. As the geologist of my young
days wrote, he had one eye upon fact, and
the other on Genesis ; at present, he wise-
ly keeps both eyes on fact, and ignores
the pentateuchal mythology altogether.
The publication of the 'Principles of
Geology ' brought upon its illustrious au-
thor a period of social ostracism ; the in-
struction given to our children is based
upon those principles. Whewell had the
courage to attack Lyell's fundamental
assumption (which surely is a dictate of
common sense) that we ought to exhaust
known causes before seeking for the ex-
planation of geological phenomena in
causes of which we have no experience.
But geology has advanced to its present
state by working from Lyell's * axiom ;

* Perhaps I ought rather to say Buffon's axiom.
For that great naturalist and -writer embodied the
principles of sound geology in a pithy phrase of the

IN THE LAST HALF-CENTUEY. 137

and, to this day, the record of the strati-
fied rocks affords no proof that the inten-
sity or the rapidity of the causes of change
has ever varied, between wider limits, than
those between which the operations of
nature have taken place in the youngest
geological epochs.

An incalculable benefit has accrued to
geological science from the accurate and
detailed surveys, which have now been
executed by skilled geologists employed
by the Governments of all parts of the
civilised world. In geology, the study of
large maps is as important as it is said to
be in politics ; and sections, on a true
scale, are even more important, in so far
as they are essential to the apprehension
of the extraordinary insignificance of geo-
logical perturbations in relation to the
whole mass of our planet. It should never

Theorie de la Terre : ' Pour juger de ce qui est arrive,
et meme de ce qui arrivera, nous n'avons qu'a examiner
ce qui arrive.'

138 THE ADVANCE OF SCIENCE

be forgotten that what we call ' catastro-
phes,' are, in relation to the earth, changes,
the equivalents of which would be well
represented by the development of a few
pimples, or the scratch of a piu, on a
man's head. Vast regions of the earth's
surface remain geologically unknown ;
but the area already fairly explored is
many times greater than it was in 1837 ;
and, in many parts of Europe and the
United States, the structure of the super-
ficial crust of the earth has been investi-
gated with great minuteness.

The parallel between Biology and Ge-
ology, which I have drawn, is further
illustrated by the modern growth of that
branch of the science known as Petrology,
which answers to Histology, and has made
the microscope as essential an instrument
to the geological as to the biological in-
vestigator.

The evidence of the importance of
causes now in operation has been wonder-

IK THE LAST HALF- CENTURY. 139

fully enlarged by the study of glacial
phenomena ; by that of earthquakes and
volcanoes ; and by that of the efficacy of
heat and cold, wind, rain, and rivers as
agents of denudation and transport. On
the other hand, the exploration of coral
reefs and of the deposits now taking place
at the bottom of the great oceans, has
proved that, in animal and plant life, we
have agents of reconstruction of a potency
hitherto unsuspected.

There is no study better fitted than
that of geology to impress upon men of
general culture that conviction of the un-
broken sequence of the order of natural
phenomena, throughout the duration of
the universe, which is the great, and per-
haps the most important, effect of the
increase of natural knowledge.

THE END.

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