of visible and tangible masses, had been shown to hold good not only
of terrestrial bodies, but of all those which constitute the visible
universe, and the movements of the macrocosm had thus been expressed
by a general mechanical theory, there remained a vast number of
phenomena, such as those of light, heat, electricity, magnetism, and
those of the physical and chemical 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 mechanical 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 imponderable substance, _caloric_; as a thing which was
absorbed by bodies when they were wanned, and was given out as they
cooled; and which, moreover, was capable of entering into a sort of
chemical combination 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 out, by rubbing them together, was practically illimitable. This
result brought philosophers face to face with the contradiction of
supposing that a finite body could contain an infinite quantity of
another body; but it was not until 1843, that clear and unquestionable
experimental proof was given of the fact that there is a 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 became the starting-point of the modern doctrine of the
conservation of energy. Molar motion had appeared to be destroyed 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 _molecular_ motion, or motion of the smallest particles of
a body, which constitutes heat. The loss of the masses is the gain of
their particles.
[Sidenote: Earlier approaches towards doctrine of conservation.]
Before 1843, however, the doctrine of conservation of energy had been
approached Bacon's chief contribution to positive science is the happy
guess (for the context shows that it was little more) that heat may be
a mode of motion; Descartes 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 thermal energy.
Again, the discovery of voltaic electricity, and the marvellous
development of knowledge, in that field, effected by such men as Davy,
Faraday, Oersted, Ampère, 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 mechanical
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 exhibited 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 'Correlation 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.[I] Such a
failure on the part of a contemporary, of great acquirements 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.
[Sidenote: What this doctrine is.]
I have pointed out that the growth of clear and definite views
respecting the constitution of matter has led to the conclusion that,
so far as natural agencies are concerned, it is ingenerable and
indestructible. In so far as matter may be conceived to exist in a
purely passive state, it is, imaginably, older than motion. 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 receives 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 impulse, on the other, and will possess _kinetic
energy_, in virtue of which it will not only continue to move for ever
if unimpeded, but if it impinges on another such particle, it will
impart more or less of its motion, to the latter. Let it be conceived
that the particle acquires a tendency to move, and that nevertheless
it does not move. It is then in a condition totally different from
that in which it was at first. A cause competent to produce motion 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 motion.
While the restraint lasts, the energy of the particle is merely
potential; and the case supposed illustrates what is meant by
_potential energy_. In this contrast of the potential with the actual,
modern physics is turning to account the most familiar of Aristotelian
distinctions--that between dunamis and energeia.
That kinetic energy appears to be imparted 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 cannot be explained, but must be taken as an ultimate fact
about which, explicable or inexplicable, there can be no doubt.
Strictly speaking, we have no direct apprehension of any other cause
of motion. But experience furnishes innumerable examples of the
production of kinetic energy in a body previously at rest, when no
impact is discernible as the cause of that energy. 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
strictly dependent on the relative positions of the two. Hence the
phrase _energy of position_, which is frequently used as equivalent to
potential energy. If a stone is picked up and held, say, six feet
above the ground, it has _potential energy_, because, if let go, it
will immediately begin to move towards the earth; and this energy may
be said to be _energy of position_, because it depends upon the
relative position of the earth and the stone. The stone is solicited
to move but cannot, so long as the muscular strength of the holder
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 falling.
Hence the energy which was exerted, 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 energy, 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.
Taking this as a very broad and general 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 appearance, there is nothing either pushing or
pulling it towards the earth, or the earth towards it; and yet it is
quite certain that the stone tends to move towards the earth and the
earth towards the stone, in the way defined by the law of gravitation.
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
'repulsive' in the other. And such attractive or repulsive forces are
often spoken of as if they were real things, capable of exerting a
pull, or a push, upon 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 summit 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 operation, 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, except the
bob, were abolished, it would move for ever in the direction of a
tangent 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 constitute 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 its swing, the bob
has a certain amount of potential energy; as it descends it gradually
exchanges this for kinetic energy, until at the centre it possesses an
equivalent 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 energy. Thus, on the whole transaction, nothing is either
lost or gained; the quantity of energy is always the same, but it
passes from one form into the other.
To all appearance, the phenomena exhibited by the pendulum are not to
be accounted for by impact: in fact, it is usually assumed that
corresponding phenomena would take place if the earth and the pendulum
were situated in an absolute vacuum, and at any conceivable distance
from, one another. If this be so, it follows that there must be two
totally different kinds of causes of motion: the one impact--a _vera
causa_, of which, to all appearance, we have constant experience; the
other, attractive or repulsive 'force'--a metaphysical entity which is
physically 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 repulsive forces, without troubling
themselves about the philosophical difficulties which it involves. But
this has not always been the case; and the attempt of Le Sage, in the
last century, to show that the phenomena of attraction and repulsion
are susceptible of explanation by his hypothesis of bombardment by
ultra-mundane particles, whether tenable or not, has the great merit
of being an attempt to get rid of the dual conception of the causes
of motion which has hitherto prevailed. On this hypothesis, the
hammering 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 hammering 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 energy which I have endeavored to
illustrate is thus defined by the late Clerk Maxwell:
'The total energy of any body or system 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
indestructible 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 material, are all molar or molecular motions, these are included
under the general law. A living body is a machine by which energy is
transformed in the same sense as a steam-engine is so, and all its
movements, molar and molecular, are to be accounted 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 doctrine of the conservation of energy applies.
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 inexplicable 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 between the oldest speculations and the
newest doctrines of physical philosophers. But there is no such
resemblance between the ancient and modern views of motion and its
causes, except in so far as the conception of attractive and repulsive
forces may be regarded 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 between ancient and modern
physical science lies in the ascertainment of the true laws of statics
and dynamics in the course of the last three centuries; and in the
invention of mathematical methods of dealing with all the consequences
of these laws. The ultimate aim of modern physical science is the
deduction of the phenomena exhibited by material bodies from
physico-mathematical first principles. Whether the human intellect is
strong enough to attain the goal set before it may be a question, but
thither will it surely strive.
[Sidenote: (3) Evolution.]
The third great scientific event of our time, the rehabilitation of
the doctrine of evolution, is part of the same tendency of increasing
knowledge to unify itself, which has led to the doctrine of the
conservation of energy. And this tendency, again, is mainly a product
of the increasing strength conferred by physical investigation on the
belief in the universal validity of that orderly relation of facts,
which we express by the so-called 'Laws of Nature.'
[Sidenote: Early stages of this theory]
The growth of a plant from its seed, of an animal from its egg, the
apparent origin of innumerable living things from mud, or from the
putrefying remains of former organisms, had furnished the earlier
scientific thinkers with abundant analogies suggestive of the
conception of a corresponding method of cosmic evolution from a
formless 'chaos' to an ordered world which might either continue for
ever or undergo dissolution into its elements before starting on a new
course of evolution. It is therefore no wonder that, from the days of
the Ionian school onwards, the view that the universe was the result
of such a process should have maintained itself as a leading dogma of
philosophy. The emanistic theories which played so great a part in
Neoplatonic philosophy and Gnostic 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 ecclesiastical scheme of
creation, as an account of that which actually was its manner of
coming into existence. In the eighteenth century, Kant put forth a
remarkable 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 seventeenth and eighteenth centuries; the
speculations of Leibnitz in the 'Protogaea' and of Buffon in his
'Théorie de la Terre;' the sober and profound reasonings 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
practically 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 Maillet made the first
serious attempt to apply the doctrine to the living world. In the
latter part of it, Erasmus Darwin, Goethe, Treviranus, and Lamarck
took up the work more vigorously 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
evolution were silenced, if not answered, by the alliance of the
greatest naturalist of the age with their ecclesiastical opponents.
Catastrophism, a short-sighted teleology, and a still more
short-sighted orthodoxy, joined forces to crush evolution.
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
proved to have occurred, in the course of the secular changes which
have taken place during the deposition of the stratified rocks. The
publication of 'The Principles 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 account 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 Agassiz, was
doomed to help the cause he hated. Agassiz not only maintained the
fact of the progressive advance in organisation 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.
[Sidenote: Darwin]
Although little acquainted with biological 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
history of physiology, of comparative anatomy and of the
palætiological sciences, vividly reproduce the controversies of the
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 favorite objection that Darwin's 'Origin of Species' is nothing
but a new version of the 'Philosophie 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 'development' 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 admitted as
a matter of fact; the selective influence of conditions, which no one
could deny to be a matter of fact, when his attention was drawn to the
evidence; and the occurrence of great geological changes which also
was matter of fact; could be used as the only necessary postulates 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 publication 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
profitable than in those of Darwin himself. His publications on the
effects of domestication in plants and animals, on the influence of
cross-fertilisation, on flowers as organs for effecting such
fertilisation, on insectivorous plants, on the motions of plants,
pointed out the routes of exploration 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. Not much has been added to the nebular hypothesis, since the
time of Laplace, except that the attempt to show (against that
hypothesis) that all nebulæ are star clusters, has been met by the
spectroscopic proof of the gaseous condition of some of them.
Moreover, physicists of the present generation appear now to accept
the secular cooling of the earth, which is one of the corollaries of
that hypothesis. In fact, attempts 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 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 application to living organisms. The
occurrence of successive forms of life upon our globe is an historical
fact, which cannot be disputed; and the relation of these successive
forms, as stages of evolution of the same type, is established in
various cases. The biologist has no means of determining 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.
[Sidenote: and philosophy]
Evolution as a philosophical doctrine 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 'Synthetic
Philosophy' of Mr. Herbert Spencer. Comment on that great undertaking
would not be in place here. I mention it because, so far as I know, it
is the first attempt to deal, on scientific principles, with modern
scientific facts and speculations. For the 'Philosophic positive' of
M. Comte, with which Mr. Spencer's system of philosophy is sometimes
compared, though it professes a similar object, is unfortunately
permeated by a thoroughly unscientific spirit, and its author 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, postulates the fixity of the rules of operation of the
causes of motion in the material universe. If all kinds of matter are
modifications of one kind, and if all modes of motion are derived from
the same energy, the orderly evolution of physical nature out of one
substratum and one energy implies 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
disorder. But it is possible to raise the question whether this
universe of simplest matter and definitely operating energy, which
forms our hypothetical starting point, may not itself be a product of
evolution 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 disposed to
take refuge in 'ignoramus et ignorabimus.'
[Sidenote: Other achievements in physical science.]
The execution of my further task, the indication of the most important
achievements in the several branches of physical science during the
last fifty years, is embarrassed by the abundance of the objects of
choice; and by the difficulty which everyone, but a specialist in each
department, must find in drawing a due distinction between discoveries
which strike the imagination by their novelty, or by their practical
influence, and those unobtrusive but pregnant observations and
experiments 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.
[Sidenote: Physics and chemistry.]
In physics and chemistry, the old boundaries of which sciences are
rapidly becoming effaced, one can hardly go wrong in ascribing a
primary value to the investigations into the relation between the
solid, liquid, and gaseous states of matter 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
electric arc; and the most refractory gases have been forced to assume
the liquid, and even the solid, forms by the combination 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 intermediation
of a condition in which it is neither truly solid nor truly liquid.
Theoretical and experimental investigations have concurred in the
establishment of the view that a gas is a body, the particles of which
are in incessant rectilinear motion at high velocities, colliding with
one another and bounding back when they strike the walls of the
containing vessel; and, on this theory, the already ascertained
relations of gaseous 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 experimentation on the phenomena which attend the
electric discharge and the action of radiant 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 radiometer. Already, these
investigations have afforded an unexpected insight into the
constitution of matter and its relations 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 investigations into the absorption of
radiant heat proceeding from different sources by solid, fluid, and
gaseous bodies. And it is a curious example of the interconnection of
the various branches of physical science, that some of the results
thus obtained have proved of great importance in meteorology.
[Sidenote: The spectroscope.]
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 recognised. 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 suddenly and immensely enlarged our power of overcoming the
obstacles which almost infinite minuteness on the one hand, and almost
infinite distance on the other, have hitherto opposed to the
recognition of the presence and the condition of matter. One
eighteen-millionth of a grain of sodium 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 constitution not only of the
sun, but of the farthest of those fixed stars and nebulæ which afford
sufficient light to affect the eye, or the photographic plate, of the
inquirer.
[Sidenote: Electricity.]
The mathematical and experimental elucidation of the phenomena of
electricity, and the study of the relations of this form of energy
with chemical and thermal action, had made extensive progress before
1837. But the determination of the influence of magnetism on light,
the discovery of diamagnetism, of the influence of crystalline
structure on magnetism, and the completion of the mathematical theory
of electricity, all belong to the present 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 delicacy and precision for the quantitative determination of
electrical phenomena. The voltaic battery has received vast
improvements; while the invention of magneto-electric engines and of
improved means of producing ordinary electricity has provided 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
science. The idea of the practicability of establishing a
communication between distant points, by means of electricity, could
hardly fail to have simmered in the minds of ingenious men since,
well nigh a century ago, experimental proof was given that electric
disturbances could be propagated 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 consideration. In its
influence on the course 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 removing the
ignorant and baneful prejudices of nation against nation, province
against province, and class against class; of assuring that social
order which is the foundation of progress, which has redeemed 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 ancient
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
telegraph. 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 highly interesting scientific fact. At the present day,
the galvano-plastic art is a great industry; and, in combination with
photography, promises to be of endless service 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 electrical 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
ordinary sense instantaneous, is recorded. The duration of the winking
of an eye is a proverbial expression for an instantaneous action;
but, by the help of the revolving 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 second exhibited.
In fact, these instruments may be said to be time-microscopes. Such
appliances have not only effected a revolution in physiology, by the
power of analysing the phenomena of muscular and nervous activity
which they have conferred, but they have furnished new methods of
measuring the rate of movement 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
deeply into the penetralia of nature, as does the sense of sight.
[Sidenote: Photography as an instrument of science.]
That light exerts a remarkable influence in bringing about certain
chemical 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
'daguerreotypes' were both cumbrous and costly, and photography would
never have attained its present important development had not the
progress of invention substituted 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
accessory to the methods of recording motions and lapse of time
already in existence. 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 physicist, not
only does it record spectroscopic phenomena with unsurpassable ease
and precision, but it has revealed the existence of rays having
powerful chemical energy, or 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 complicated objects may be represented,
without that possibility of error which is inherent in the work of the
draughtsman. In fact, in many cases, the stern impartiality of
photography is an objection to its employment: it makes no distinction
between the important and the unimportant; and hence photographs of
dissections, for example, are rarely so useful as the work of a
draughtsman who is at once accurate and intelligent.
[Sidenote: Astronomy,]
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
immediate confirmation of that determination, in the year 1846, by
observers who turned their telescopes into the part of the heavens
indicated as its place, constitute a remarkable testimony of nature to
the validity of the principles of the astronomy of our time. In
addition, so many new asteroids have been added to those which were
already known to circulate in the place which theoretically should be
occupied by a planet, between Mars and Jupiter, 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 spectroscopy. It has not only thrown wonderful
light upon the physical and chemical constitution of the sun, fixed
stars, and nebulæ, and comets, but it holds out a prospect of
obtaining definite evidence as to the nature of our so-called
elementary bodies.
[Sidenote: its relation to geology.]
The application of the generalisations of thermotics to the problem of
the duration 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 demonstration 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 intimate
relation with geology. Geology, in fact, proves that, in the course of
the past history of the earth, the climatic conditions of the same
region have been widely different, and seeks the explanation of this
important truth from the sister sciences. 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 accompaniment of gigantic glaciers, obtained
in the northern hemisphere, as far south as Switzerland and Central
France, are as well established as any truths of science. But, whether
the explanation of these extreme variations in the mean temperature of
a great part of the northern hemisphere is to be sought in the
concomitant changes in the distribution of land and water surfaces of
which geology affords evidence, or in astronomical conditions, such as
those to which I have referred, is a question which must await its
answer from the science of the future.
[Sidenote: Biological sciences.]
[Sidenote: The 'cell theory.']
Turning now to the great steps in that progress which the biological
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 generalisation known as the 'cell theory,'
the application and extension of which by a host of subsequent
investigators has revolutionised morphology, development, and
physiology. Thanks to the immense series of labors thus inaugurated,
the following fundamental truths have been established.
[Sidenote: Fundamental truths established.]
All living bodies contain substances of closely similar physical and
chemical composition, which constitute the physical 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 aggregate of minute portions of such substance, of similar
structure, called cells, each cell having its own life independent of
the others, though influenced by them.
All the morphological characters of animals 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 animals and plants--assimilation,
secretion, excretion, motion, generation--are the expression of the
activities of the cells considered as physiological units. Each
individual, among the higher animals and plants, is a synthesis of
millions of subordinate 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 demarcation between animals and plants.
The intimate structure, and the modes of change, in the cells of the
two are fundamentally 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 development 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 devised.
[Sidenote: Spontaneous generation disproved.]
The popular belief in abiogenesis, or the so-called 'spontaneous'
generation of the lower forms of life, which was accepted by all the
philosophers of antiquity, held its ground down to the middle of the
seventeenth century. Notwithstanding the frequent citation of the
phrase, wrongfully attributed to Harvey, 'Omne vivum ex ovo,' that
great physiologist believed 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 experiments,
demonstrated that, in a great number of cases of supposed spontaneous
generation, the animals which made their appearance owed their origin
to the ordinary process of reproduction, and thus shook the ancient
doctrine to its foundations. In the middle of the eighteenth century,
it was revived, in a new form, by Needham and Buffon; but the
experiments of Spallanzani enforced the conclusions of Redi, and
compelled the advocates of the occurrence of spontaneous generation to
seek evidence for their hypothesis 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, the supposed
evidence of abiogenesis was untrustworthy.
During the present epoch, the question, whether living matter can be
produced in any other way than by the physiological activity of other
living matter, has been discussed afresh with great vigor; and the
problem has been investigated by experimental methods of a precision
and refinement unknown to previous investigators. The result is that
the evidence in favor of abiogenesis has utterly broken down, in every
case which has been properly tested. So far as the lowest and minutest
organisms are concerned, it has been proved that they never make their
appearance, if those precautions by which their germs are certainly
excluded are taken. And, in regard 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 totally
different significance. Whether not-living matter may pass, or ever
has, under any conditions, passed into living matter, without the
agency of pre-existing 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
matters stand, it is equally justifiable to regard the physical world
as a sort of dual monarchy. The kingdoms of living matter 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.
[Sidenote: Morphology.]
In the department of anatomy and development, a host of accurate and
patient inquirers, aided by novel methods of preparation, which
enable the anatomist to exhaust the details of visible structure and
to reproduce them with geometrical precision, have investigated every
important group of living animals and plants, no less than the fossil
relics of former faunæ and floræ. An enormous addition has thus been
made to our knowledge, especially 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, vertebrates from
invertebrates, cryptogams from phanerogams, have either been filled
up, or shown to have no theoretical significance. The question of the
position of man, as an animal, has given rise to much disputation,
with the result of proving that there is no anatomical or
developmental 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 Linnæus
has been proved to be more in accordance with the facts than those of
most of his successors.
[Sidenote: Anthropology.]
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 animal
life, has given rise to a special branch of biology, known, as
Anthropology, which has grown with great rapidity. Numerous societies
devoted to this portion of science have sprung up, and the energy of
its devotees has produced a copious literature. The physical
characters of the various races of men have been studied with a
minuteness and accuracy heretofore unknown; and demonstrative
evidence of the existence of human contemporaries 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 archæology; and the striking investigations 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 which 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 of
embryology were explored, the likeness and unlikeness of individual
development 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 others. A classification which
shall represent 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
palæontology has given us far more insight than we yet possess, into
the historical facts of the case. Much of the speculative 'phylogeny,'
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 direction, it is often extremely useful; but,
when the product of such speculation is placed on a level with those
generalisations 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 'Sceptical Chemist,'
and I am inclined to think that, at the present day, a 'Sceptical
Biologist' might exert an equally beneficent influence.
[Sidenote: Physiology.]
Whoso wishes to gain a clear conception of the progress of physiology,
since 1837, will do well to compare Müller's 'Physiology,' which
appeared in 1835, and Drapiez's edition of Richard's 'Nouveaux
Eléments de Botanique,' published in 1837, with any of the present
handbooks of animals and vegetable physiology. Müller's work was a
masterpiece, unsurpassed since the time of Haller, and Richard's book
enjoyed a great reputation at the time; but their successors transport
one into a new world. That which characterises the new physiology is
that it is permeated by, and indeed based upon, 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 organisms, 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
assumption that the physical and chemical 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 phenomena
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 molecular
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 accumulation of solid knowledge, which has been
effected, is correspondingly great. For the first time in the history
of science, physiologists are now in the position to say that they
have arrived at clear and distinct, though by no means complete,
conceptions of the manner in which the great functions of
assimilation, respiration, secretion, 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
manifestations of activity, either within itself or in other organs,
has been largely elucidated.
[Sidenote: Practical value of physiological discovery.]
I have pointed out, in an earlier part of this chapter, that the
history of all branches of science proves that they must 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 scientific 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.
But within that time, they have already rendered highly important
services by the exploration of the phenomena of parasitism. 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 investigations, 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' theory
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
prophylactic measures, such as vaccination, which formerly rested on a
merely empirical basis; and it has been extended to other diseases
with excellent results. Further, just as the discovery of the cause of
scabies proved the absurdity of many of the old prescriptions for the
prevention 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 humanity. Unless the fanaticism of philozoic 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 England
was devastated by the plague; cleanliness 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 empirically, and almost in
the dark, has reduced 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 pestilences, passing one's offspring through the fire
to Moloch seems humanity, compared 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 involved in the search
for means of guarding them.
[Sidenote: Scientific exploration.]
An immense extension has been effected in our knowledge of the
distribution of plants and animals; and the elucidation of the causes
which have brought about that distribution has been greatly advanced.
The establishment of meteorological observations by all civilised
nations, has furnished a solid foundation to climatology; while a
growing sense of the importance of the influence of the 'struggle for
existence' affords a wholesome check to the tendency to overrate the
influence of climate on distribution. Expeditions, such as that of the
Challenger,' 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
Governments, and have obtained stores of information of the greatest
value. For the first time, we are in possession of something like
precise knowledge of the physical 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 accumulations of
snow and ice, in polar and mountainous 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 referred to diluvial catastrophes, but
it has suggested new methods of accounting for various puzzling facts
of distribution.
[Sidenote: Palæontology.]
Palæontology, which treats of the extinct 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 wonderful
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 Flora is but the last term of a long series of equally
numerous contemporary species, which have succeeded one another, by
the slow and gradual substitution of species for species, in the vast
interval of time which has elapsed between the deposition of the
earliest fossiliferous strata and the present day. There is no
reasonable ground for believing that the oldest remains yet obtained
carry us even near the beginnings of life. The impressive warnings of
Lyell against hasty speculations, based upon negative evidence, have
been fully justified; time after time, highly organised types have
been discovered in formations 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, wherever
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, 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 fossiliferous
formations; and thus show that progressive development is a
contingent, and not a necessary result, of the nature of living
matter.
[Sidenote: Geology.]
Geology is, as it were, the biology of 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 effected the progress
of the earth from its earliest 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 century ago, is
presented by the complete emancipation of the modern geologist from
the controlling and perverting influence of theology, all-powerful at
the earlier date. As the geologist of my young days wrote, he had one
eye upon fact, and the other on Genesis; at present, he wisely keeps
both eyes on fact, and ignores the pentateuchal mythology altogether.
The publication of the 'Principles of Geology' brought upon its
illustrious author a period of social ostracism; the instruction 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 explanation of geological phenomena in causes of which
we have no experience. But geology has advanced to its present state
by working from Lyell's[J] axiom; and, to this day, the record of the
stratified rocks affords no proof that the intensity 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 geological perturbations in relation
to the whole mass of our planet. It should never be forgotten that
what we call 'catastrophes,' 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 pin, 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 superficial crust of the earth has been investigated
with great minuteness.
The parallel between Biology and Geology, 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 investigator.
The evidence of the importance of causes now in operation has been
wonderfully 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 unbroken sequence of the
order of natural phenomena, throughout the duration of the universe,
which is the great, and perhaps the most important, effect of the
increase of natural knowledge.