[Sidenote: Recent industrial progress]
The most obvious and the most distinctive features of the History of
Civilisation, during the last fifty years, is the wonderful increase
of industrial production by the application of machinery, the
improvement of old technical processes and the invention of new ones,
accompanied by an even more remarkable development of old and new
means of locomotion and intercommunication. By this rapid and vast
multiplication of the commodities and conveniences of existence, the
general standard of comfort has been raised, the ravages of pestilence
and famine have been checked, and the natural obstacles, which time
and space offer to 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 organisation of the commonwealth against those of political or
social anarchy, thus effected, have exerted an influence on the
present and future fortunes of mankind the full significance of which
may be divined, but cannot, as yet, be estimated at its full value.
[Sidenote: caused by the increase of physical science]
This revolution--for it is nothing less--in the political and social
aspects of modern civilisation has been preceded, accompanied, and in
great measure caused, by a less obvious, but no less marvellous,
increase of natural knowledge, and especially of that part of it which
is known as Physical Science, in consequence of the application of
scientific 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, Literature, and
Art, in ancient Greece; and, after being dammed up for a thousand
years, once more began to flow three centuries ago.
[Sidenote: Greek and mediæval science.]
It may be doubted if even-handed justice, as free from fulsome
panegyric as 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 standstill by the decay
and disruption of the Roman Empire, the consequent disorganisation 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 Middle Ages. And, notwithstanding sporadic attempts to recall men
to the investigation 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
Archimedes, Hipparchus, and Ptolemy, of Aristotle and of Galen,
naturally enough arose among the astronomers and the 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 conjunction 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, arithmetic, and music,
as one of the four branches of advanced education; and, in this
respect, it is only just to them to observe that they were far in
advance of those who sit in their seats. The school men considered no
one to be properly educated unless he were acquainted with, at any
rate, one branch of physical science. We have not, even yet, reached
that stage of enlightenment.
[Sidenote: Further advance after Renaissance.]
In the early decades of the seventeenth century, the men of the
Renaissance could show that they had already put out to good interest
the treasure bequeathed to them by the Greeks. They had produced the
astronomical system of Copernicus, with Kepler's great additions; 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 associations for
the investigation of nature, the models of all subsequent academies
and scientific societies, had been founded, while the literary skill
and biting wit of Galileo had made the great scientific questions of
the day not only intelligible, but attractive, to the general public.
[Sidenote: Francis Bacon.]
In our own country, Francis Bacon, had essayed to sum up the past of
physical 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 already achieved by
the true instaurators of physical science; yet the majestic eloquence
and the fervid vaticinations of one who was conspicuous alike by the
greatness of his rise and the depth of his fall, drew the attention of
all the world to the 'new birth of Time.'
[Sidenote: The defect of his method.]
But it is not easy to discover satisfactory evidence that the 'Novum
Organum' had any direct beneficial influence on the advancement of
natural knowledge. No 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
'anticipation of nature' by the invention of hypotheses based on
incomplete inductions, 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
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 foresaw, 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 Bacon's pleadings for science is the gathering of
fruit'--the importance of winning solid material advantages by the
investigation of Nature and the desirableness of limiting the
application of scientific methods of inquiry to that field.
[Sidenote: Hobbes.]
[Sidenote: Descartes.]
Bacon's younger contemporary, Hobbes, casting aside the prudent
reserve of his 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 phenomena 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 imaginary, knowledge. The
'Principles of Philosophy' 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 Hobbes, René
Descartes, not only in his immortal 'Discours de la Méthode' and
elsewhere, went down to the foundations of scientific certainty, but,
in his 'Principes de Philosophie,' indicated where the goal of
physical science really lay. However, Descartes was an eminent
mathematician, and it would seem that the bent of his mind led him to
overestimate the value of deductive reasoning from general principles,
as much as Bacon had underestimated 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 Newton, 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
investigation should be pursued.
[Sidenote: For a time the progress without fruits.]
The progress of science, during the first century after Bacon's death,
by means verified his sanguine prediction of 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 apparent. Sixty years after Bacon's death, Newton had crowned
the long labors of the astronomers and the physicists, by coordinating
the phenomena of solar motion throughout the visible universe into one
vast system; but the 'Principia' helped no man to either wealth or
comfort. Descartes, Newton, and Leibnitz had opened up new worlds to
the mathematician, but the acquisitions of their genius enriched only
man's ideal estate. Descartes had laid the foundations of rational
cosmogony and of physiological psychology; Boyle had produced models
of experimentation in various branches of physics and chemistry;
Pascal and Torricelli had weighed the air; Malpighi and Grew, Ray and
Willoughby had done work of no less importance in the biological
sciences; but weaving and spinning were carried on with the old
appliances; nobody could travel faster by sea or by land than at any
previous time in the world's history, and King George could 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 chemistry, geology, and biology; but this deepening and
broadening of natural knowledge 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 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
accumulation 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.'
[Sidenote: Its recent effect on life.]
But, a little later, that growth of knowledge beyond imaginable
utilitarian 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 dependent upon men's efforts, which is
subservient to their wants, and which would disappear if man's
shaping and guiding hand were withdrawn. Every mechanical artifice,
every chemically pure substance employed in manufacture, every
abnormally fertile race of plants, or rapidly growing and fattening
breed of animals, is a part of the new Nature created by science.
Without it, the most densely populated regions of modern Europe and
America must retain their primitive, sparsely inhabited, agricultural
or pastoral condition; it is the foundation of our wealth and the
condition of our safety from submergence 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. During the
last fifty years, this new birth of 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.
[Sidenote: These results often too much regarded;]
What wonder, then, if these astonishing fruits of the tree of
knowledge are too often regarded by both friends and enemies as the
be-all and end-all of science? What wonder if some eulogise, and
others revile, the new philosophy for its utilitarian ends and its
merely material triumphs?
[Sidenote: for scientific research rarely directed to practical ends]
In truth, the new philosophy deserves neither the praise of its
eulogists, nor the blame of its slanderers. As I have pointed 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 latter
part of the eighteenth and the first decade of the nineteenth
century, of Herschel, of Laplace, of Young, of Fresnel, of Oersted, of
Cavendish, of Lavoisier, of Davy, of Lamarck, of Cuvier, of Jussieu,
of Decandolle, of Werner and of Hutton, suffices to indicate the
strength of physical science in the age immediately preceding that of
which I have to treat. But of which of these great men can it be said
that their labors were directed to practical ends? I do not call to
mind even an invention of practical utility which we owe to any of
them, except the safety lamp of Davy. Werner certainly paid attention
to mining, and I have not forgotten James Watt. But, though some of
the most important of the improvements by which Watt converted the
steam-engine, invented long before his time, into the obedient slave
of man, were suggested and guided by his acquaintance with scientific
principles, his skill as a practical mechanician, and the efficiency
of Bolton's workmen had quite as much to do with the realisation of
his projects.
[Sidenote: but instigated by love of knowledge]
In fact, the history of physical science teaches (and we cannot too
carefully take the lesson to heart) that the practical advantages,
attainable through its agency, never have been, and never will be,
sufficiently 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
supreme 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 philosopher, sometimes
intentionally, much more often unintentionally, lights upon something
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 being
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.
[Sidenote: It is in its turn assisted by industrial improvements.]
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
alongside truth, or even wealth alone. Such a profession is as
respectable as any other. And quite as little do I desire to ignore
the fact that, if industry owes a heavy debt to science, it has
largely repaid the 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 knowledge in the
schools of Athens and of Alexandria, it has often struck me[A] that
where the Greeks did wonders was in just those branches of science,
such as geometry, astronomy, and anatomy, which are susceptible of
very considerable development without any, or any but the simplest,
appliances. 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 investigators to obtain, at
comparatively little cost, microscopes, telescopes, and all the
exquisitely delicate apparatus for determining weight and measure and
for estimating the lapse of time with exactness, which they now
command. If science has rendered the colossal development of modern
industry possible, beyond a doubt industry has done no less for modern
physics 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 warfare, 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 technical education, is reacting upon science in a manner
which will, assuredly, stimulate its future growth to an incalculable
extent. It has become obvious that the interests of science and of
industry are 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 industry facilitates those
experimental investigations, 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
philosophers who 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 adolescence in the
seventeenth and eighteenth centuries, remains true of its riper age in
these latter days of the nineteenth century. The great steps in its
progress have been made, are made, and will be made, by men who seek
knowledge simply because they crave for it. They have their
weaknesses, their follies, their vanities, 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.[B] 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 them; and men of
great natural gifts have failed, absolutely or relatively, because
they lacked this one thing needful.
[Sidenote: True aim and method of research.]
To anyone who knows the business of investigation practically, Bacon's
notion of 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.[C] 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. Newton said that he made his discoveries by
'intending' his mind 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 capacities 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.
* * * * *
[Sidenote: Progress from 1837 to 1887.]
I am conscious that in undertaking to progress give even the briefest
sketch of the progress of physical science, in all its branches,
during the last half-century, I may be thought to have exhibited more
courage than discretion, and perhaps more presumption than either. So
far as physical science is concerned, the days of Admirable 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.
Nor 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 commencement of the
Victorian epoch. As to subsequent events, there are numerous
excellent summaries of the progress of various branches of science,
especially up to 1881, which was the jubilee year of the British
Association.[D] 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 escaping serious errors is as good
as that of anyone else, who might have been persuaded to undertake the
somewhat perilous 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 myself to the
work done, without saying anything 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 undesirable when
one is dealing with contemporaries. 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 Israelites, who
struggled with one another in the field, addressed to Moses--'Who made
thee a prince and a judge over us.'
[Sidenote: The aim of physical science]
Physical science is one and indivisible. Although, for practical
purposes, it is convenient to mark it out into the primary regions of
Physics, Chemistry, and Biology, and to subdivide these into
subordinate provinces, yet the method of investigation and the
ultimate object of the physical inquirer are everywhere the same.
[Sidenote: the discovery of the rational order of the universe]
The object is the discovery of the rational order which pervades the
universe, the method consists of observation and experiment (which is
observation under 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 incorrect than the assumption one
sometimes meets with, that physics has one method, chemistry another,
and biology a third.
[Sidenote: It is based on postulates]
All physical science starts from certain postulates. One of them is
the objective existence of a material world. It is assumed that the
phenomena which are comprehended under this name have a 'substratum'
of extended, impenetrable, mobile substance, which exhibits the
quality known as inertia, and is termed matter.[E] Another postulate
is the universality of the law of causation; that nothing 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 state at any preceding moment. Another is that any
of the rules, or so-called 'laws of nature,' by which the relation of
phenomena is truly defined, is true for all time. The validity of
these postulates is a problem of metaphysics; they are neither
self-evident nor are they, strictly speaking, demonstrable. The
justification of their employment, as axioms of physical philosophy,
lies in the circumstance that expectations logically based upon them
are verified, or, at any rate, not contradicted, whenever they can be
tested by experience.
[Sidenote: and uses hypotheses.]
Physical science therefore rests on verified or uncontradicted
hypotheses; and, such being the case, it is not surprising that a
great condition of its progress has been the invention of verifiable
hypotheses. 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 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 Nature,' that is, by the invention of hypotheses,
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.
[Sidenote: Fruitful use of an hypothesis even when wrong.]
The geocentric system of astronomy, with its eccentrics and its
epicycles, was an hypothesis utterly at variance with fact, which
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; and the undulatory theory, which has superseded the
corpuscular theory and has proved one of the most fertile of
instruments of research, is based on the hypothesis of the existence
of an 'ether,' the properties of which are defined 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
observation, 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 enlarged. Or, to put the matter in another way, a doctrine
which is untrue absolutely, may, to a very great extent, be
susceptible of an interpretation in accordance with the truth. At a
certain period in the history of astronomical science, the assumption
that the planets move in circles was true enough to serve the purpose
of correlating such observations as were then possible; after Kepler,
the assumption that they move in ellipses became true enough in regard
to the state of observational astronomy at that time. We say still
that the orbits of the planets are ellipses, because, for all ordinary
purposes, that is a sufficiently near approximation to the truth; but,
as a matter of fact, the centre of gravity of a planet describes
neither an ellipse or any other simple curve, but an immensely
complicated undulating line. It may fairly be doubted whether any
generalisation, or hypothesis, based upon physical data is absolutely
true, in the sense that a mathematical 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 interpret nature, as if it were absolutely
true.
The development of every branch of physical knowledge presents three
stages which, in their logical relation, are successive. 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 motion. The last two stages constitute
_Natural Philosophy_ in its original sense. In this region, the
invention of verifiable hypotheses is not only permissible, but is one
of the conditions of progress.
[Sidenote: and mutual assistance of observation, experiment, and
speculation.]
Historically, no branch of science has followed this order of growth;
but, from the dawn of exact knowledge to the present day, observation,
experiment, and speculation have gone hand in hand; and, whenever
science has halted or strayed from the right path, it has been, either
because its votaries have been content with mere unverified or
unverifiable speculation (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.
[Sidenote: Recognition of these truths in recent times, and consequent
progress.]
The progress of physical science, since the revival of learning, is
largely due to the fact that men have gradually learned to lay aside
the consideration of unverifiable 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 behind
phenomena, but as a symbolical language, by the aid of which nature
can be interpreted in terms apprehensible by our intellects. And if
physical science, during the last fifty years, has attained dimensions
beyond all former precedent, and can exhibit achievements of greater
importance than any former such period can show, it is because able
men, animated by the true scientific spirit, carefully trained in the
method of science, and having at their disposal immensely improved
appliances, have devoted themselves to the enlargement of the
boundaries of natural knowledge in greater number than during any
previous half-century of the world's history.
[Sidenote: The three great achievements. Doctrines of (1) molecular
constitution of matter, (2) conservation of energy, (3) evolution.]
I have said that our epoch can produce achievements in physical
science of greater moment than any other has to show, advisedly; and
I think that there are three great products of our time which justify
the assertion. One of these is that doctrine concerning the
constitution of matter which, for want of a better name, I will call
'molecular;' the second is the doctrine of conservation of energy; the
third is the doctrine of evolution. Each of these was foreshadowed,
more or less distinctly, in former periods of the history of science;
and, so far is either from being the outcome of purely inductive
reasoning, that it would be hard to overrate the influence of
metaphysical, and even of theological, considerations upon the
development of all three. The peculiar 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; 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
phenomena.
[Sidenote: (1) Molecular constitution of matter.]
In the early decades of this century, a number of important truths
applicable, in part, to matter in general, and, in part, to particular
forms of matter, had been ascertained by the physicists and chemists.
The laws of motion of visible and tangible, or _molar_, matter had
been worked out to a great degree of refinement and embodied in the
branches 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
assumption that all such masses of matter possessed inertia and were
susceptible of acquiring 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.
[Sidenote: The two theories as to matter.]
With respect to the ultimate constitution of these masses, the same
two antagonistic opinions which had existed since the time of
Democritus and of Aristotle were still face to face. According to the
one, matter was discontinuous and consisted of minute indivisible
particles or atoms, separated by a universal vacuum; according to the
other, it was continuous, and the finest distinguishable, or
imaginable, particles were scattered through the attenuated general
substance of the plenum. A rough analogy to the latter case would be
afforded by granules of ice diffused through water; to the former,
such granules diffused through absolutely empty space.
[Sidenote: Reassertion by Dalton of atomic theory.]
In the latter part of the eighteenth century, the chemists had arrived
at several very important generalisations respecting 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 varied only in
its perceptibility by our senses. The course of investigation further
proved that a certain number of the chemically separable kinds of
matter were unalterable by any known means (except in so far as they
might be made to change their state from solid to fluid, or _vice
versâ_), 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 compounds, bodies always unite in a definite
proportion by weight, or in simple multiples of that proportion, and
that, if any one body were taken as a standard, every other could have
a number assigned to it as its proportional combining weight. It was
on this foundation of fact that Dalton based his re-establishment of
the old atomic hypothesis on a new empirical foundation. It is
obvious, that if elementary matter consists of indestructible and
indivisible particles, each of which constantly preserves the same
weight relatively 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 reception of the undulatory theory of
light necessitated 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 substance 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 material
substance, Democritic atomism is at an end and Cartesian continuity
takes its place.
[Sidenote: The real value of hypothesis; it predicates the existence
of units of matter.]
The real value of the new atomic hypothesis, however, did not lie in
the two 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, material bodies
consist of definite minute masses, each of which, so far as physical
and chemical processes of division go, may be regarded 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
divisibility, so such a minute mass is the unit of physico-chemical
science--that smallest material particle which under any given
circumstances acts as a whole.[F]
The doctrine of specific heat originated 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 quantities. 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 inversely proportional to their
combining weights. Thus a definite relation was established 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 decomposition. The phenomena of
isomorphism showed a relation between the units and crystalline forms;
certain units are thus able to replace others in a crystalline body
without altering its form, and others are not.
Again, the laws of the effect of pressure 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 Daltonian hypothesis, and led to the bold
speculation known as the law of Avogadro--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 hypothesis was
incorrect--perhaps it is not exactly true in any form; but it is
hardly too much to say that chemistry and molecular physics would
never have advanced 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, was the creation of a system of
symbolic notation, which not only made the nature of chemical
compounds and processes easily 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 schematism of Linnæus were to zoölogy and
botany.
[Sidenote: In biology a like theory of molecularstructure.]
Side by side with these advances arose in another, which also has a
close parallel in the history of biological science. If the unit of a
compound is made up by the aggregation of elementary units, the notion
that these must have some sort of definite arrangement inevitably
suggests itself; and such phenomena as double decomposition pointed,
not only to the existence 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 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
without 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
chemistry enabled these ideas to be represented with precision; and
they acquired an immense importance, when the improvement of methods
of analysis, which took place about the beginning of our period,
enabled the composition of the so-called 'organic' bodies to be
determined with, rapidity and precision.[G] A large proportion of
these compounds contain not more than three or four elements, of which
carbon is the chief; but their number is very great, and the diversity
of their physical and chemical properties is astonishing. The
ascertainment of the proportion of each element in these compounds
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_ compounds,
the appeal to diversity of arrangement of the identical component
units was the only obvious way out of the difficulty. Here, again,
hypothesis 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 together; 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, theoretically, that certain non-existent compounds ought
to be producible, and he proceeds to produce them.
It is largely because the chemical theory 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 that
singular conception of 'bonds' invented to colligate the facts of
'valency' or 'atomicity,' the first of which took some time to make
its way; while the second fell into oblivion, for many years after it
was propounded, for lack of empirical 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 entirely 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 absorption of heat when they are dissociated, and a host
of other molecular phenomena, have been shown to be deducible from the
dynamical and statical principles which apply to molar motion and
rest; and the tendency of physico-chemical science is clearly towards
the reduction of the problems of the world of the infinitely little,
as it already has reduced those of the infinitely great world, to
questions of mechanics.[H]
In the meanwhile, the primitive atomic theory, which has served as the
scaffolding 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
interatomic matterless vacuum. 'Atoms' appear 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
endless 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.
[Sidenote: Elementary bodies]
The greater number of the so-called 'elementary' bodies, now known,
had been discovered before the commencement of our epoch; and it had
become apparent 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 like one another as they
were unlike the rest. Chlorine, iodine, bromine, and fluorine 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 natural groups, such as
those into which animals and plants fall.
[Sidenote: fall into different series.]
Recently this subject has been taken up afresh, 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
heaviest, as 240--the series does not exhibit one continuous
progressive modification 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, d, e, f, g, h, i, k,_ &c.,
but
_a, b, c, d_, A, B, C, D, alpha, beta, gamma, delta, &c.;
so that it is said to express a _periodic 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 _w_ 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 corresponding terms of which have analogous
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 delta
_c_ C gamma
_b_ B beta
_a_ A alpha
- ----- ---------
_w_ _w + x_ _w + x + y_
[Sidenote: The possibility of a primary form of matter.]
This is a conception with, which biologists 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 understood to mean evolution
from a common prototype. It is difficult to imagine that in the
not-living world they are devoid of significance. Is it not possible,
nay probable that they may mean the evolution of our 'elements' from a
primary undifferentiated 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-chemical science.
In fact, the so-called 'vortex-ring' hypothesis 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 speaking, 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 interesting to remark that this
hypothesis reminds 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 between the modern and the ancient notion of a
distinction between primary and derivative matter is, to a certain
extent, real. For this ethereal 'Urstoff' of the modern corresponds
very closely with the prhôtê hylê of Aristotle, the _materia prima_ of
his mediæval followers; while matter, differentiated into our
elements, is the equivalent of the first stage of progress towards the
heschhatê hylê, 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 under all conditions, whether
natural or artificial, 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. Theoretically, 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 possible 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 universe, is of no more weight
against the possibility of change in them, in the infinity of
antecedent time, than the constancy of species in Egypt, since the
days of Rameses or Cheops, is evidence of their immutability during
all past epochs of the earth's history. It seems safe to prophesy
that the hypothesis of the evolution 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 foundation.
[Sidenote: The old and the new atomic theory.]
It may perhaps occur to the reader that the boasted progress of
physical science does not come to much, if our present conceptions of
the fundamental nature of matter are expressible in terms employed,
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, they indicate definite
physical conceptions, susceptible of mathematical treatment, and
giving rise to innumerable deductions, the value of which can be
experimentally tested. The old notions produced little more than
floods of dialectics; the new are powerful aids towards the increase
of solid knowledge.
[Sidenote: (2) Conservation of energy.]
Everyday observation shows that, of the bodies which compose the
material 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, exhibit a
constant movement, regular in amount and direction, for which no
external cause appears. Others, as stones and smoke, seem also to move
of themselves 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 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 extremely 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 observed by saying that bodies, which are free to move, tend
towards their proper places. All these seem to be natural motions,
dependent on the inherent faculties, 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
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 ancient
Greeks, and remained dominant until the age of Galileo. The
publication of the 'Principia' of Newton, in 1686-7, marks the epoch
at which the progress of mechanical physics had effected a complete
revolution of thought on these subjects. By this time, it had been
made clear that the old generalisations were either incomplete or
totally erroneous; that a body, once set in motion, will continue to
move in a straight 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, when a body in motion acts as a
cause of motion on another, the latter gains as much as the former
loses, and _vice versâ_. It is to be noted, however, that while, in
contradistinction to the ancient idea of the inherent tendency 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 is 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 virtue of which, any two such particles, without any external
impression of motion, or intermediate material agent, were supposed to
tend to approach or remove 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 investigation, attained in the seventeenth
century, was the proof and quantitative estimation of physical
inertia. In the old philosophy, 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 matter 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 is complex. In part, it
contains a corollary 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 distance
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, 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 the body.
To this the name of 'mass' has been given. And since it seems
reasonable 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 demonstrable
that, at any given time and place, the relative mass of any two bodies
is expressed by the ratio of their weights.
[Sidenote: Mechanical theory of heat.]