THE KNOWABLE AND UNKNOWABLE—BRAIN AND THOUGHT.
Basis of knowledge—Perception—Constitution of brain—White and
grey matter—Average size and weight of brains—European, negro,
and ape—Mechanism of perception—Sensory and motor nerves—Separate
areas of brain—Sensory and motor centres—Abnormal states of
brain—Hypnotism—Somnambulism—Trance—Thought-reading—Spiritualism—Reflex
action—Ideas how formed—Number and space—Creation
unknowable—Conceptions based on perceptions—Metaphysics—Descartes,
Kant, Berkeley—Anthropomorphism—Laws of nature.
Before entering on the higher subjects of religions and philosophies,
it is well to arrive at some precise idea of the limits of human
knowledge, and of the boundary line which separates the knowable from the
unknowable. The ultimate basis of all knowledge is perception. Without
an environment to create impressions, and an organ to receive them,
we should know absolutely nothing. What is the environment and what
the organ of human knowledge? The environment is the whole surrounding
universe, or, in the last analysis, the motions, or changes of motion,
by which the objects in that universe make impressions on the recipient
organ. The organ is the grey matter of that large nervous agglomeration,
the brain. But here I must at the outset make two reservations. In the
first place I do not define how these impressions are made. In all
ordinary cases they are made through the channels of the senses; but it
is possible that in certain exceptional cases vibrations in the brain,
causing perceptions, may be conveyed to it through the nerves in other
ways. In somnambulism, for instance, it seems to be an ascertained fact
that a somnambulist with closed eyes securely bandaged can walk in the
dark and avoid obstacles as well as if guided by the sight in full
daylight. There is a great deal of evidence also that in artificial
somnambulism, otherwise called mesmerism or hypnotism, and also in what
is called thought-reading, perceptions may be conveyed from one brain to
another otherwise than by the usual methods of speech or writing. But
these phenomena, however far they may be extended, do not affect the
position that impressions on the brain are the essential condition of
thought. If the grey matter of the brain is deficient or diseased the
mind is affected, and beyond a certain point becomes extinct.
The second and more important reservation is, that although mind and
all its qualities are thus indissolubly connected with matter, it by
no means follows that they are matter or mere qualities of it. In the
case of the atoms and energies, we know absolutely nothing of their real
essence, and cannot form even a conception of what they are, how they
came there, or what will become of them. It is the same with mind, soul,
or self: we feel an instinctive certainty of their existence, as we do of
that of matter; and we can trace their laws and manifestations under the
conditions in which they are known to us, viz. those of association with
matter and motion in the brain. But of their real essence or existence we
know nothing, and it is as unscientific to affirm as to deny. Directly
we pass beyond the boundary of such knowledge as really can be known
by human faculty, and stand face to face with the mystery of the Great
Unknown, we can only bow our heads with reverence and say with the poet,
Behold, I know not anything.
I hope thus to steer safely between Scylla and Charybdis—between the
arid rocks of materialism and the whirling eddies of spiritualism.
Materialist and spiritualist seem to me very like two men disputing as to
the existence of life in the sun. ‘No,’ argues the former; ‘for the known
conditions there are totally inconsistent with any life we can conceive.’
‘Yes,’ says the other; ‘for the belief fits in with many things which
I earnestly wish to believe respecting a Supreme Being and a future
existence.’ To the first I say, ignorance is not evidence; to the second,
wishes are not proofs. For myself, while not quarrelling with those more
favoured mortals who have, or fancy they have, superior knowledge, I
can only say that I really know nothing; and this being the case, I see
no use in saying that I know, and think it both more truthful and more
modest to confess the limitation of my faculties.
With this caution I return to the field of positive knowledge. The brain,
spinal marrow, and nerves consist of two substances: one white, which
constitutes the great mass consisting of tubes or fibres; the other grey,
which is an aggregation of minute cells, so minute that it has been
computed that there are several millions of them in a space no larger
than a sixpence. The bulk of this grey nerve-tissue is found in the
higher animals, and especially in man, in the outside rind which covers
the brain, and its amount is greatly increased by the convolutions of
that organ giving a greater extent of covering surface. In fact the
convolutions of the average human brain give as much grey matter in a
head of average size, as would be given by a head of four times the size
if the brain were a plane surface. The extent of the convolutions is,
therefore, a sure sign of the extent of intellect. They are more numerous
and deeper in the European than in the negro; in the negro than in the
chimpanzee; in the anthropoid ape than in the monkey or lemur. This grey
nerve-tissue is the organ by which impressions from without are turned
into perceptions, volitions, and evolutions of nerve force. The white
matter is simply the medium of transmission, or we may say the telegraph
wires by which the impressions are conveyed to the head office and the
answers sent. The cell-tissue of the grey matter is thus emphatically
the organ of the mind. In fact, if it did not sound too materialistic,
we might call thought a secretion of the grey matter, only in saying
so we must bear in mind that it is only a mode of expressing the fact
that the two invariably go together; and that if we say with the German
philosopher ‘Ohne Phosphor kein Gedank,’ it does not mean that thought
and phosphorus are identical, but simply that the condition on which
thought depends is that of the existence of a material organ of which
phosphorus is an ingredient.
That this grey nerve-tissue is really the organ of thought has been
firmly established by numerous experiments both in man and the lower
animals. Injuries to it, or diseases in it, invariably affect what is
called the mind; while considerable portions of the white matter may be
removed without affecting the thinking and perceptive powers. A certain
amount of it is indispensable for the existence of intellect; the more
there is of it as the brain increases in size and the convolutions become
deeper, the greater is the intellect; when these fall below certain
dimensions intellect is extinguished and we have idiocy. The average
brain of the male white European weighs 49½ ounces, of the negro a
little under 47. The maximum brains which have been accurately weighed
and measured, are those of Cuvier and Daniel Webster, the weight of
the former being 64⅓ ounces, and the capacity of the latter being 122
cubic inches; while the average capacity of the Teutonic race, including
English, Germans, and Americans, is 92 inches, of the negro 83, and of
the Australian and Hottentot 75. The brain of the idiot seldom weighs
over 23 ounces, and the minimum weight consistent with a fair degree of
intelligence is about 34 ounces.
The mechanism by which correspondence is kept up between the living
individual and the surrounding universe is very simple—in reality, as
simple as that of any ordinary electric circuit. In the most complex
case, that of man, there are a number of nerve-endings, or small lumps
of protoplasm, embedded in the tissues all over the body, or highly
specialised and grouped together in separate organs such as the eye
and ear, from which a nerve-fibre leads direct to the brain, or to the
spinal cord and so up to the brain. These nerve-endings receive the
different vibrations by which outward energy presents itself, which
propagate a current or succession of vibrations of nerve-energy along the
nerve-fibre. This nerve-fibre is a round thread of protoplasm covered
by a white sheath of fatty matter which insulates it like the wire of
a submarine telegraph coated with gutta-percha. This nerve-wire leads
up to a nerve-centre, consisting of two corpuscles of protoplasm: the
first or sensory, a smaller one, which is connected by branches with the
second, a much larger one, called the motor, from which a much larger
nerve-fibre or wire proceeds, which terminates in a mass of protoplasm
firmly attached to a muscle. Thus, a sensation is propagated along the
sensory nerve to the sensory nerve-centre, whence it is transmitted to
the motor-centre, which acts as an accumulator of stored-up energy,
a large flow of which is sent through the large conductor of the
motor-nerve to the muscle, which it causes to contract and thus produces
motion. It is thus that the simpler involuntary actions are produced
by a process which is purely mechanical. In the more complex cases, in
which consciousness and will are involved, the process is essentially
the same, though more complicated. The message is transmitted to the
brain, where it is received by a cluster of small sensory cells or
nerve-centres, which are connected with another cluster of fewer and
larger motor-centres, often at some distance from them, by a network
of interlacing fibres. But it is always a case of a single circuit of
wires, batteries, and accumulators, adapted for receiving, recording,
and transmitting one sort of vibrations caused by and producing one sort
of energy, and one only. The brain does not act as a whole, receiving
indiscriminately impressions of light, sound, and heat; but by separate
organs for each, located in separate parts of it. It is like a great
central office, in one room of which you have a printing instrument
reading off and recording messages sent through an electric telegraph; in
another a telephone; in a third a self-registering thermometer, and so
on. And the same for the motor-centres and nerves. One set is told off to
move the muscles of the face, another those of the arms, others for the
legs and body, and so forth. This is further complicated by the fact that
the brain like the rest of the body has two sides, a right and left, and
that in some cases the motor-apparatus is doubled, each working only on
one side, while in others the same battery and wires serve for both. As a
rule the right hemisphere of the brain works the muscles of the left side
of the body, and _vice versâ_, so that an injury to one side of the brain
may paralyse the voluntary motion of the limbs on the opposite side,
leaving in a perfect condition those on its own side.
In the case of the higher functions involving thought, the upper part of
the brain, which performs these functions, seems to be a sort of duplex
machine, so that we have two brains capable of thinking, just as we
have two eyes capable of seeing. It is a remarkable fact that the areas
of the brain which are appropriated to the lowest and most instinctive
functions, which appear first, lie lowest, and as the functions rise the
position of their nerve-centres rises with them. Thus, at the very base
of the frontal convolutions at the lowest end of the fissure of Rolando,
we find the motor areas for the lower part of the face, by which the
lowest animals and the new-born infant perform their solitary function
of sucking and swallowing. Higher up are the centres in the right and
left brains for moving the upper limbs, that is, for seizing food and
conveying it to the mouth, which is the next function in the ascending
scale. Next above these are the centres for moving the lower limbs
and for co-ordinating the motions of the arms and legs, marking the
progression of an organism which can pursue and catch as well as eat its
food. And still higher are the centres which regulate the motions of the
trunk and body in correspondence with those of the limbs; while highest
of all, at the front and hind ends of the enveloping cortex of the brain,
come the organs of the intellectual faculties.
It is easy to see that this corresponds with the progression of the
individual, for the infant sucks and cries for food from the first day,
soon learns to extend its hand and grasp objects, but takes some time
to learn to walk, and still longer to perform exercises like dancing or
riding, in which the motions of the whole body have to be co-ordinated
with those of the limbs. And as the development of the individual is an
epitome of the evolution of life from protoplasm, we may well suppose
that the brain was developed in this order from its first origin in
a swelling at the end of the spinal cord as we find it in the lowest
vertebrates.
It is a singular fact that the particular motor area which gives the
faculty of articulate speech lies in a small patch of about one and a
half square inches on the left side of the lower portion of the first
brain. If this is injured, the disease called aphasia is produced, in
which the patient loses the power of expressing ideas by connected words.
The corresponding area on the right side cannot talk; but in left-handed
persons this state of things is reversed, and the right side, which is
generally aphasial, can be taught to speak in young people, though not in
the aged.
Higher up in the cortex, or convoluted envelope of the brain, come the
areas for hearing and seeing, the latter being the more extensive. These
areas are filled mainly by a great number of sensory nerve-centres or
cells, connected with one another in a very complicated network. These
seem to be connected with the multitude of ideas which are excited in the
brain by perceptions derived from the higher senses, especially that of
sight. The simple movements are produced by a few large motor-centres,
which have only one idea and do only one thing, whether it be to move the
leg or the arm. But a sensation from sight often calls up a multitude of
ideas. Suppose you see the face of one with whom some fifty years ago you
may have had some youthful love passages, but your lives drifted apart,
and you now meet for the first time after these long years, how many
ideas will crowd on the mind, how many nerve-cells will be set vibrating,
and how many nerve-currents set coursing along intricate paths! No wonder
that the nerve-corpuscles are numerous and minute, and the nerve-channels
many and complicated.
When we come to the seats of the intellectual faculties the question
becomes still more obscure. They are probably situated in the hinder and
front parts of the surface of the brain, and depend on the grey matter
consisting of an immense number of minute sensory cells. It has been
computed that there are millions in the area of a square inch, and they
are all in a state of the most delicate equilibrium, vibrating with the
slightest breath of nervous impression. They depend for their activity
entirely on the sensory perceptive centres, for there is no consciousness
in the absence of sensory stimulation, as in dreamless sleep. Perception,
however caused, whether by outward stimulation of real objects, or by
former perceptions revived by memory, sends a stream of energy through
the sense-area, which expands, like a river divided into numerous
channels, fertilising the intellectual area, where it is stored up by
memory, giving us the idea of continual individual existence, and by some
mysterious and unknown process becoming transformed into consciousness
and deliberate thought. And conversely the process is reversed when what
we call will is excited, and the small currents of the intellectual area
are concentrated by an effort of attention and sent along the proper
nerve-channels to the motor-centres, whose function it is to produce
the desired movement. This mechanical explanation, it will be observed,
leaves entirely untouched the question of the real essence and origin of
these intellectual faculties, as to which we know nothing more than we do
of the real essence and origin of life, of matter, and of energy.
A very curious light however is thrown on them by phenomena which
occur in abnormal states of the brain, as in trance, somnambulism, and
hypnotism. In the latter, by straining the attention on a given object or
idea, such as a coin held in the hand or a black wafer on a white wall,
the normal action of the brain is, in the case of many persons—perhaps
one out of every three or four—thrown out of gear, and a state induced
in which the will seems to be annihilated, and the thoughts and actions
brought into subjection to the will of another person. In this state
also a cataleptic condition of the muscles is often induced, in which
they acquire enormous strength and rigidity. In somnambulism outward
consciousness is in a great measure suspended, and the somnambulist
lives for the time in a walking dream which he acts and mistakes for
reality. In this state old perceptions, scarcely felt at the time, seem
to revive, as in dreams, with such wonderful vividness and accuracy that
the somnambulist in acting the dream does things altogether impossible in
the waking state. Thus an ignorant Scotch servant-maid is said to have
recited half a chapter of the Hebrew version of the Old Testament: the
explanation being that she had been in the service of a Scotch minister,
who was studying Hebrew, and who used to walk about his room reciting
this identical passage. It would seem as if the brain were like a very
delicate photograph plate, which takes accurate impressions of all
perceptions, whether we notice them or not, and stores them up ready to
be reproduced whenever stronger impressions are dormant and memory by
some strange caprice breathes on the plate.
Most wonderful, however, are some of the phenomena of trance. In this
case it really seems as if two distinct individuals might inhabit the
same body. Jones falls into a trance and dreams that he is Smith. While
the trance lasts he acts and talks as Smith, he really is Smith, and
even addresses his former self Jones as a stranger. When he wakes from
the trance he has no recollection of it, and takes up the thread of
his own life, just as if he had dozed for a minute instead of being
in a trance for hours. But if he falls into a second trance, days or
weeks afterwards, he takes up his trance life exactly where he dropped
it, absolutely forgetting his intermediate real life. And so he may go
on alternating between two lives, with two separate personalities and
consciousnesses, being to all intents and purposes now Jones and now
Smith. If he died during a trance, which would he be, Jones or Smith? The
question is more easily asked than answered; but it certainly appears
as if with one mode of motion in the same brain you might have one mind
and personal identity associated with it, and with another mode of motion
different ones.
It would take me too far, and the facts are too doubtful, to investigate
the large class of cases included under the terms thought-reading,
telepathy, psychism, and spiritualism. It may suffice to say that there
is a good deal of evidence for the reality of very curious phenomena,
but none of any real weight for their being caused by any spiritualistic
or supernatural agency. They all seem to resolve themselves into the
assertion that under special conditions the perceptions of one brain can
be reproduced in another otherwise than by the ordinary medium of the
senses, and that in such conditions a special sort of cataleptic energy
or psychic force may be developed. The amount of negative evidence is
of course enormous, for it is certain that in millions upon millions
of cases thought cannot be read, things are not seen beyond the range
of vision, and coincidences do not occur between deaths and dreams or
visions. Neither can tables be turned, nor heavy bodies lifted, without
some known form of energy and a fulcrum at which to apply it.
This borderland of knowledge is, therefore, best left to time, which is
the best test of truth. That which is real will survive, and be gradually
brought within the domain of science and made to fit in with other facts
and laws of nature. That which is unreal will pass away, as ghosts
and goblins have done, and be forgotten as the fickle fashion changes
of superstitious fancy. In the meantime we shall do better to confine
ourselves to ascertained facts and normal conditions.
It is pretty certain that although the brain greatly preponderates as
an organ of mind in man and the higher animals, the grey tissue in the
spinal marrow and nervous ganglia exercises a limited amount of the
same functions proportionate to its smaller quantity. The reflex or
automatic actions, such as breathing, are carried on without reference
to the brain, and the messages are received and transmitted through the
local offices without going to the head office. This is the case with
many complicated motions which originated in the brain, but have become
habitual and automatic, as in walking, where thought and conscious
effort only intervene when something unusual occurs which requires a
reference to the head office; and in the still more complex case of the
piano-player, who fingers difficult passages correctly while thinking of
something else or even talking to a bystander.
Indeed, in extreme cases, where experiments on the brain have been
tried on lower animals, it is found that it can be entirely removed
without destroying life, or affecting many of the actions which require
perception and volition. Thus, when the brain has been entirely removed
from a pigeon, it smoothes its feathers with its bill when they have been
ruffled, and places its head under its wing when it sleeps; and a frog
under the same conditions, if held by one foot endeavours to draw it
away, and if unsuccessful, places the other foot against an obstacle in
order to get more purchase in the effort to liberate itself.
So much for the organ of mind; the other factor, that of outward
stimulus, is still more obvious. If thought cannot exist without grey
nerve-tissue, neither can it without impressions to stimulate that
tissue. A perfect brain, if cut off from all communication with the
external universe, could no more think and have perceptions, than
impressions from without could generate them without the appropriate
nerve-tissue. Once generated, the mind can store them up by memory,
control them by reason, and gradually evolve from them ever higher and
higher ideas and trains of reasoning, both in the individual and the
species:—in the individual passing from infancy to manhood, partly by
heredity from ancestors, and partly by education—using the word in the
large sense of influences of all sorts from the surrounding environment;
in the species, by a similar but much slower development from savagery to
civilisation.
Thus the whole fabric of arithmetic, algebra, and the higher calculi
are built up from the primitive perception of number. The earliest
palæolithic savage must have been conscious of a difference between
encountering one or two cave-bears or mammoths; and some existing races
of savages have hardly got beyond this primitive perception. Some
Australian tribes, it is said, have not got beyond three numerals, one,
two, and a great number. But by degrees the perceptions of number have
become more extensive and accurate, and the number of fingers on each
hand has been used as a standard of comparison. Thus ten, or two-hand,
the number of fingers on the two hands has gradually become the basis
of arithmetical numeration, and from this up to Sir W. Hamilton’s
‘Quaternions’ the progression is regular and intelligible. But Newton
could never have invented the differential calculus and solved the
problem of the heavens, if thousands of centuries before some primitive
human mind had not received the perception that two apples or two bears
were different from one.
In like manner geometry, as its name indicates, arises from primitive
perceptions of space, applied to the practical necessity of
land-measuring in alluvial valleys like those of the Nile and Euphrates,
where annual inundations obliterated to a great extent the dividing
lines between adjoining properties. The first perceptions of space would
take the form of the rectangle, or so many feet or paces, or cubits or
arm-lengths, forwards, and so many sideways, to give the proper area;
but as areas were irregular, it would be discovered that the triangle
was necessary for more accurate measurement. Hence the science of the
triangle, circle, and other regular forms, as we see it developed in
Euclid and later treatises on geometry, until we see it in its latest
development in speculations as to space of four dimensions.
But in all these cases we see the same fundamental principle as prevails
throughout the universe under the name of the ‘conservation of energy’;
always something out of something, never something out of nothing.
This, therefore, defines the limit of human knowledge, or boundary line
between the knowable and the unknowable. Whatever is _transformation_
according to existing laws is, whether known or unknown, at any rate,
knowable—whatever is _creation_ is unknowable. We have absolutely no
faculties to enable us to form the remotest conception of what the
essence of these primary atoms and energies really is, how they came
there, and how the laws, or invariable sequences, under which they act,
came to be impressed on them. We have no faculties, because we have
never had any perceptions upon which the mind can work. Reason and
imagination can no more work without antecedent perceptions than a bird
can fly in a vacuum.
Thus, for instance, the imagination can invent dragons, centaurs, and any
number of fabulous monsters, by piecing together fragments of perceptions
in new combinations; but ask it to invent a monster whose head shall
be that of an inhabitant of Saturn and its body that of a denizen of
Jupiter, and where is it? Of necessity all attempts to define or describe
things of which we have never had perceptions, must be made in terms of
things of which we have had perceptions, or, in other words, must be
anthropomorphic.
So far as science gives any positive knowledge as to the relations of
mind to matter, it amounts to this: That all we call mind is indissolubly
connected with matter through the grey cells of the brain and other
nervous ganglia. This is positive. If the skull could be removed without
injury to the living organism, a skilful physiologist could play with his
finger on the human brain, as on that of a dog, pigeon, or other animal,
and by pressure on different notes, as on the keys of a piano, annihilate
successively voluntary motion, speech, hearing, sight, and finally will,
consciousness, reasoning power, and memory. But beyond this physical
science cannot go. It cannot explain how molecular motions of cells of
nerve-centres can be transformed into, or can create, the phenomena of
mind, any more than it can explain how the atoms and energies to which it
has traced up the material universe were themselves created or what they
really are.
All attempts to further fathom the depths of the unknown follow a
different line, that of metaphysics, or, in other words, introspection of
mind by mind, and endeavour to explain thought by thinking. On entering
into this region we at once find that the solid earth is giving way
under our feet, and that we are attempting to fly in an extremely rare
atmosphere, if, indeed, we are not idly flapping our wings in an absolute
vacuum. Instead of ascertained facts which all recognise, and experiments
which conducted under the same conditions always give the same results,
we have a dissolving view of theories and intuitions, accepted by some,
denied by others, and changing with the changing conditions of the age,
and with individual varieties of characters, emotions, and wishes. Thus,
mind and soul are with some philosophers identical, with others mind
is a product of soul; with some soul is a subtle essence, with others
absolutely immaterial; with some it has an individual, with others a
universal, existence; by some it is limited to man, by others conceded to
the lower animals; by some located in the brain, by others in the heart,
blood, pineal gland, or dura mater; with some it is pre-existent and
immortal, with others created specially for its own individual organism;
and so on _ad infinitum_. The greatest philosophers come mostly to the
conclusion that we really know nothing about it. Thus Descartes, after
having built up an elaborate metaphysical theory as to a spiritual,
indivisible substance independent of the brain and cognisable by
self-consciousness alone, ends by honestly confessing ‘that by natural
reason we can make many conjectures about the soul, and have flattering
hopes, but no assurance.’ Kant also, greatest of metaphysicians in
demolishing the fallacies of former theories, when he comes to define his
‘noumenon,’ has to use the vaguest of phrases, such as ‘an indescribable
something, safely located out of space and time, as such not subject
to the mutabilities of those phenomenal spheres, ... and of whose
ontological existence we are made aware by its phenomenal projections,
or effects in consciousness.’ The sentence takes our breath away, and
makes us sympathise with Bishop Berkeley when he says, ‘We metaphysicians
have first raised a dust, and then complain we cannot see.’ It prepares
us also for Kant’s final admission that nothing can really be proved by
metaphysics concerning the attributes, or even the existence, of the
soul; though, on the other hand, as it cannot be disproved, its reality
may for moral purposes be assumed.
It appears, therefore, that the efforts of the sublimest
transcendentalists do not carry us one step farther than the conclusions
of the commonest common-sense, viz. that there are certain fundamental
conditions of thought, such as space, time, consciousness, personal
identity, and freedom of will, which we cannot explain, but cannot get
rid of. The sublimest speculations of a Plato and a Kant bring us back
to the homely conclusions of the old woman in the nursery ballad, in
whose mind grave questions as to her personal identity were raised by the
felonious abstraction of the lower portion of her petticoat.
If I be I, as I think I be,
I’ve a little dog at home, and he’ll know me.
It is a safe ‘working hypothesis’ that when I go home in the afternoon,
my wife, children, and little dog will recognise me as being ‘I myself
I;’ but why or how I am I, whether I was I before I was born, or shall
be so after I am dead, I really know no more than the little dog who wags
his tail and yelps for joy when he recognises my personal identity as
something distinct from his own, when he sees me coming up the walk.
Our conceptions, therefore, are necessarily based on our perceptions,
and are what is called anthropomorphic. The term has almost come to
be one of reproach, because it has so often been applied to religious
conceptions of a Deity with human, though often not very humane,
attributes; but, if considered rightly, it is an inevitable necessity
of any attempt to define such a being or beings. We can only conceive
of such as of a magnified man, indefinitely magnified no doubt, but
still with a will, intelligence, and faculties corresponding to our own.
The whole supernatural or miraculous theory of the universe rests on
the supposition that its phenomena are, in a great many cases, brought
about, not by uniform law, but by the intervention of some Power, which,
by the exercise of will guided by intelligent design, alters the course
of events and brings about special effects. As long as the theory is
confined to knowable transformations of existing things, like those
which are seen to be affected by human will, it is not necessarily
inconceivable or irrational. Inferring like effects from like causes,
the hypothesis was by no means unreasonable that thunder and lightning,
for instance, were caused by some angry invisible power in the clouds.
On the contrary, the first savage who drew the deduction was a natural
philosopher who reasoned quite justly from his assumed premises. Whether
the premises were true or not was a question which could only be
determined centuries later by the advance of accurate knowledge.
When do we say we know a thing? Not when we know its essence and primary
origin, for of these the wisest philosopher is as ignorant as the rudest
savage; but when we know its place in the universe, its relation to other
things, and can fit it in to that harmonious sequence of events which is
summed up in what are called Laws of Nature. The highest knowledge is
when we can trace it up to its earliest origin from existing matter and
energy, and follow it downwards so as to be able to predict its results.
The force of gravity affords a good illustration of this knowledge, both
where it comes up to, and where it falls short of, perfection.
Newton’s law leaves nothing to be desired as regards its universal
application and power of prediction; but we do not yet fully understand
its mode of action or its relation to other forms of energy. It is
probable that some day we may be able to understand how the force of
gravity appears to act instantaneously at a distance, and how all the
transformable forces, gravity, light, heat, electricity, and molecular or
atomic forces, are but different manifestations of one common energy. But
in the meantime we know this for certain, that the law of gravity is not
a local or special phenomenon, but prevails universally from the fixed
stars to the atoms, from the infinitely great to the infinitely small.
This is a _fact_ to which all other phenomena, which are true facts and
not illusions, must conform.
In like manner, if we find in caves or river-gravels, under circumstances
implying enormous antiquity, and associated with remains of extinct
animals, rude implements so exactly resembling those in use among
existing savages, that if the collection in the Colonial Exhibition
of stone celts and arrow-heads used by the Bushmen of South Africa
were placed side by side with one from the British Museum of similar
objects from Kent’s Cavern or the caves of the Dordogne, no one but an
expert could distinguish between them, the conclusion is inevitable
that Devonshire and Southern France were inhabited at some remote
period by a race of men not more advanced than the Bushmen. Any theory
of man’s origin and evolution which is to hold water must take account
of this fact and square with it. And so of a vast variety of facts
which have been reduced to law and become certainly known during the
last half-century. A great deal of ground remains unexplored or only
partially explored; but sufficient has been discovered to enable us
to say that what we know we know thoroughly, and that certain leading
facts and principles undoubtedly prevail throughout the knowable
universe, including not only that which is known, but that which is as
yet partially or wholly unknown. For instance, the law of gravity, the
conservation of energy, the indestructibility of matter, and the law of
evolution, or development from the simple to the complex.