Chapter III: Spiritual or Moral Development (2)

Now there is nothing in this process which necessarily eludes the
power of mind as we know it. An intellect the same kind as our own,
would, if only sufficiently expanded, be able to follow the whole
process from beginning to end. No entirely new intellectual faculty
would be needed for this purpose. The duly expanded mind would see
in the process and its consummation an instance of the play of
molecular force. It would see every molecule placed in its position
by the specific attractions and repulsions exerted between it and
other molecules. Nay, given the grain and its environment, an
intellect the same in kind as our own, but sufficiently expanded,
might trace out _à priori_ every step of the process, and by the
application of mechanical principles would be able to demonstrate
that the cycle of actions must end, as it is seen to end, in the
reproduction of forms like that with which the operation began. A
similar necessity rules here to that which rules the planets in
their circuits round the sun.

You will notice that I am stating my truth strongly, as at the
beginning we agreed it should be stated. But I must go still
further, and affirm that in the eye of science the animal body is
just as much the product of molecular force as the stalk and ear of
corn, or as the crystal of salt or sugar. Many of its parts are
obviously mechanical. Take the human heart, for example, with its
exquisite system of valves, or take the eye or the hand. Animal
heat, moreover, is the same in kind as the heat of a fire, being
produced by the same chemical process. Animal motion, too, is as
directly derived from the food of the animal, as the motion of
Trevethyck’s walking-engine from the fuel in its furnace. As regards
matter, the animal body creates nothing; as regards force, it
creates nothing. Which of you by taking thought can add one cubit to
his stature? All that has been said regarding the plant may be
re-stated with regard to the animal. Every particle that enters into
the composition of the muscle, a nerve, or a bone, has been placed
in its position by molecular force. And unless the existence of law
in these matters be denied, and the element of caprice be
introduced, we must conclude that, given the relation of any
molecule of the body to its environment, its position in the body
might be predicted. Our difficulty is not with the quality of the
problem, but with its complexity; and this difficulty might be met
by the simple expansion of the faculties which man now possesses.
Given this expansion, and given the necessary molecular data, and
the chick might be deduced as rigorously and as logically from the
egg as the existence of Neptune was deduced from the disturbances of
Uranus, or as conical refraction was deduced from the undulatory
theory of light.

You see I am not mincing matters, but avowing nakedly what many
scientific thinkers more or less distinctly believe. The formation
of a crystal, a plant, or an animal, is in their eyes a purely
mechanical problem, which differs from the problems of ordinary
mechanics in the smallness of the masses and the complexity of the
processes involved. Here you have one half of our dual truth; let us
now glance at the other half. Associated with this wonderful
mechanism of the animal body we have phenomena no less certain than
those of physics, but between which and the mechanism we discern no
necessary connection. A man, for example, can say I feel, I think, I
love; but how does consciousness infuse itself into the problem? The
human brain is said to be the organ of thought and feeling; when we
are hurt the brain feels it, when we ponder it is the brain that
thinks, when our passions or affections are excited it is through
the instrumentality of the brain. Let us endeavor to be a little
more precise here. I hardly imagine that any profound scientific
thinker who has reflected upon the subject exists, who would not
admit the extreme probability of the hypothesis, that for every fact
of consciousness, whether in the domain of sense, of thought, or of
emotion, a certain definite molecular condition is set up in the
brain; that this relation of physics to consciousness is invariable,
so that, given the state of the brain, the corresponding thought or
feeling might be inferred; or, given the thought or feeling, the
corresponding state of the brain might be inferred. But how
inferred? It is at bottom not a case of logical inference at all,
but of empirical association. You may reply that many of the
inferences of science are of this character; the inference, for
example, that an electric current of a given direction will deflect
a magnetic needle in a definite way; but the cases differ in this,
that the passage from the current to the needle, if not
demonstrable, is thinkable, and that we entertain no doubt as to the
final mechanical solution of the problem; but the passage from the
physics of the brain to the corresponding facts of consciousness is
unthinkable. Granted that a definite thought and a definite
molecular action in the brain occur simultaneously, we do not
possess the intellectual organ, nor, apparently, any rudiment of the
organ, which would enable us to pass by a process of reasoning from
the one phenomenon to the other. They appear together, but we do not
know why. Were our minds and senses so expanded, strengthened, and
illuminated as to enable us to see and feel the very molecules of
the brain; were we capable of following all their motions, all their
groupings, all their electric discharges, if such there be; and were
we intimately acquainted with the corresponding states of thought
and feeling, we should be as far as ever from the solution of the
problem. “How are these physical processes connected with the facts
of consciousness?” The chasm between the two classes of phenomena
would still remain intellectually impassable. Let the consciousness
of love, for example, be associated with a right-handed spiral
motion of the molecules of the brain, and the consciousness of hate
with a left-handed spiral motion. We should then know when we love
that the motion is in one direction, and when we hate that the
motion is in the other; but the “WHY?” would still remain
unanswered.

In affirming that the growth of the body is mechanical, and that
thought, as exercised by us, has its correlative in the physics of
the brain, I think the position of the “Materialist” is stated as
far as that position is a tenable one. I think the materialist will
be able finally to maintain this position against all attacks; but I
do not think, as the human mind is at present constituted, that he
can pass beyond it. I do not think he is entitled to say that his
molecular groupings and his molecular motions explain everything. In
reality they explain nothing. The utmost he can affirm is the
association of two classes of phenomena of whose real bond of union
he is in absolute ignorance. The problem of the connection of the
body and soul is as insoluble in its modern form as it was in the
pre-scientific ages. Phosphorus is known to enter into the
composition of the human brain, and a courageous writer has
exclaimed, in his trenchant German, “Ohne phosphor kein gedanke.”
That may or may not be the case; but even if we knew it to be the
case, the knowledge would not lighten our darkness. On both sides of
the zone here assigned to the materialist he is equally helpless. If
you ask him whence is this “matter” of which we have been
discoursing, who or what divided it into molecules, who or what
impressed upon them this necessity of running into organic forms, he
has no answer. Science also is mute in reply to these questions. But
if the materialist is confounded, and science rendered dumb, who
else is entitled to answer? To whom has the secret been revealed?
Let us lower our heads and acknowledge our ignorance, one and all.
Perhaps the mystery may resolve itself into knowledge at some future
day. The process of things upon this earth has been one of
amelioration. It is a long way from the Iguanodon and his
contemporaries to the president and members of the British
Association. And whether we regard the improvement from the
scientific or from the theological point of view as the result of
progressive development, or as the result of successive exhibitions
of creative energy, neither view entitles us to assume that man’s
present faculties end the series—that the process of amelioration
stops at him. A time may therefore come when this ultra-scientific
region by which we are now enfolded may offer itself to terrestrial,
if not to human investigation. Two-thirds of the rays emitted by the
sun fail to arouse in the eye the sense of vision. The rays exist,
but the visual organ requisite for their translation into light does
not exist. And so from this region of darkness and mystery which
surrounds us, rays may now be darting which require but the
development of the proper intellectual organs to translate them into
knowledge as far surpassing ours as ours does that of the wallowing
reptiles which once held possession of this planet. Meanwhile the
mystery is not without its uses. It certainly may be made a power in
the human soul; but it is a power which has feeling, not knowledge,
for its base. It may be, and will be, and we hope is turned to
account, both in steadying and strengthening the intellect, and in
rescuing man from that littleness to which, in the struggle for
existence or for precedence in the world, he is continually prone.

II.

On Haze and Dust.

Solar light in passing through a dark room reveals its track by
illuminating the dust floating in the air. “The sun,” says Daniel
Culverwell, “discovers atomes, though they be invisible by
candle-light, and makes them dance naked in his beams.”

In my researches on the decomposition of vapors by light, I was
compelled to remove these “atomes” and this dust. It was essential
that the space containing the vapors should embrace no visible
thing; that no substance capable of scattering the light in the
slightest sensible degree should, at the outset of an experiment, be
found in the “experimental tube” traversed by the luminous beam.

For a long time I was troubled by the appearance there of floating
dust, which, though invisible in diffuse daylight, was at once
revealed by a powerfully condensed beam. Two tubes were placed in
succession in the path of the dust: the one containing fragments of
glass wetted with concentrated sulphuric acid; the other, fragments
of marble wetted with a strong solution of caustic potash. To my
astonishment it passed through both. The air of the Royal
Institution, sent through these tubes at a rate sufficiently slow to
dry it and to remove its carbonic acid, carried into the
experimental tube a considerable amount of mechanically-suspended
matter, which was illuminated when the beam passed through the tube.
The effect was substantially the same when the air was permitted to
bubble through the liquid acid and through the solution of potash.

Thus, on the 5th of October, 1868, successive charges of air were
admitted through the potash and sulphuric acid into the exhausted
experimental tube. Prior to the admission of the air the tube was
_optically empty_; it contained nothing competent to scatter the
light. After the air had entered the tube, the conical track of the
electric beam was in all cases clearly revealed. This, indeed, was a
daily observation at the time to which I now refer.

I tried to intercept this floating matter in various ways; and on
the day just mentioned, prior to sending the air through the drying
apparatus, I carefully permitted it to pass over the tip of a
spirit-lamp flame. The floating matter no longer appeared, having
been burnt up by the flame. It was, therefore, _organic matter_.
When the air was sent too rapidly through the flame, a fine blue
cloud was found in the experimental tube. This was the _smoke_ of
the organic particles. I was by no means prepared for this result;
for I had thought, with the rest of the world, that the dust of our
air was, in great part, inorganic and non-combustible.

Mr. Valentin had the kindness to procure for me a small gas-furnace,
containing a platinum tube, which could be heated to vivid redness.
The tube also contained a roll of platinum gauze, which, while it
permitted the air to pass through it, insured the practical contact
of the dust with the incandescent metal. The air of the laboratory
was permitted to enter the experimental tube, sometimes through the
cold, and sometimes through the heated tube of platinum. The
rapidity of admission was also varied. In the first column of the
following table the quantity of air operated on is expressed by the
number of inches which the mercury gauge of the air-pump sank when
the air entered. In the second column the condition of the platinum
tube is mentioned, and in the third the state of the air which
entered the experimental tube.

State of State of
Quantity Platinum Experimental
of Air. Tube. Tube.

15 inches Cold Full of particles.

15 inches Red-hot Optically empty.

15 inches Cold Full of particles.

15 inches Red-hot Optically empty.

15 inches Cold Full of particles.

15 inches Red-hot Optically empty.

The phrase “optically empty” shows that when the conditions of
perfect combustion were present, the floating matter totally
disappeared. It was wholly burnt up, leaving not a trace of residue.
From spectrum analysis, however, we know that soda floats in the
air; these organic dust particles are, I believe, the _rafts_ that
support it, and when they are removed it sinks and vanishes.

When the passage of the air was so rapid as to render imperfect the
combustion of the floating matter, instead of optical emptiness a
fine blue cloud made its appearance in the experimental tube. The
following series of results illustrate this point:

Quantity. Platinum Tube. Experimental Tube.
15 inches, slow Cold Full of particles.
15 inches, slow Red-hot Optically empty.
15 inches, quick Red-hot A blue cloud.
15 inches, quick Intensely hot A fine blue cloud.

The optical character of these clouds was totally different from
that of the dust which produced them. At right angles to the
illuminating beam they discharged perfectly polarized light The
cloud could be utterly quenched by a transparent Nicol’s prism, and
the tube containing it reduced to optical emptiness.

The particles floating in the air of London being thus proved to be
organic, I sought to burn them up at the focus of a concave
reflector. One of the powerfully convergent mirrors employed in my
experiments on combustion by dark rays was here made use of, but I
failed in the attempt. Doubtless the floating particles are in part
transparent to radiant heat, and are so far incombustible by such
heat. Their rapid motion through the focus also aids their escape.
They do not linger there sufficiently long to be consumed. A flame
it was evident would burn them up, but I thought the presence of the
flame would mask its own action among the particles.

In a cylindrical beam, which powerfully illuminated the dust of the
laboratory, was placed an ignited spirit-lamp. Mingling with the
flame, and round its rim, were seen wreaths of darkness resembling
an intensely black smoke. On lowering the flame below the beam the
same dark masses stormed upwards. They were at times blacker than
the blackest smoke that I have ever seen issuing from the funnel of
a steamer, and their resemblance to smoke was so perfect as to lead
the most practiced observer to conclude that the apparently pure
flame of the alcohol lamp required but a beam of sufficient
intensity to reveal its clouds of liberated carbon.

But is the blackness smoke? The question presented itself in a
moment. A red-hot poker was placed underneath the beam, and from it
the black wreaths also ascended. A large hydrogen flame was next
employed, and it produced those whirling masses of darkness far more
copiously than either the spirit-flame or poker. Smoke was,
therefore, out of the question.

What, then, was the blackness? It was simply that of stellar space;
that is to say, blackness resulting from the absence from the track
of the beam of all matter competent to scatter its light. When the
flame was placed below the beam the floating matter was destroyed
_in situ_; and the air, freed from this matter, rose into the beam,
jostled aside the illuminated particles and substituted for their
light the darkness due to its own perfect transparency. Nothing
could more forcibly illustrate the invisibility of the agent which
renders all things visible. The beam crossed, unseen, the black
chasm formed by the transparent air, while at both sides of the gap
the thick-strewn particles shone out like a luminous solid under the
powerful illumination.

But here a difficulty meets us. It is not necessary to burn the
particles to produce a stream of darkness. Without actual
combustion, currents may be generated which shall exclude the
floating matter, and therefore appear dark amid the surrounding
brightness. I noticed this effect first on placing a red-hot copper
ball below the beam, and permitting it to remain there until its
temperature had fallen below that of boiling water. The dark
currents, though much enfeebled, were still produced. They may also
be produced by a flask filled with hot water.

To study this effect a platinum wire was stretched across the beam,
the two ends of the wire being connected with the two poles of a
voltaic battery. To regulate the strength of the current a rheostat
was placed in the circuit. Beginning with a feeble current the
temperature of the wire was gradually augmented, but before it
reached the heat of ignition, a flat stream of air rose from it,
which when looked at edgeways appeared darker and sharper than one
of the blackest lines of Fraunhofer in the solar spectrum. Right and
left of this dark vertical band the floating matter rose upwards,
bounding definitely the non-luminous stream of air. What is the
explanation? Simply this. The hot wire rarefied the air in contact
with it, but it did not equally lighten the floating matter. The
convection current of pure air therefore passed upwards _among the
particles_, dragging them after it right and left, but forming
between them an impassable black partition. In this way we render an
account of the dark currents produced by bodies at a temperature
below that of combustion.

Oxygen, hydrogen, nitrogen, carbonic acid, so prepared as to exclude
all floating particles, produce the darkness when poured or blown
into the beam. Coal-gas does the same. An ordinary glass shade
placed in the air with its mouth downwards permits the track of the
beam to be seen crossing it. Let coal-gas or hydrogen enter the
shade by a tube reaching to its top, the gas gradually fills the
shade from the top downwards. As soon as it occupies the space
crossed by the beam, the luminous track is instantly abolished.
Lifting the shade so as to bring the common boundary of gas and air
above the beam, the track flashes forth. After the shade is full, if
it be inverted, the gas passes upwards like a black smoke among the
illuminated particles.

The air of our London rooms is loaded with this organic dust, nor is
the country air free from its pollution. However ordinary daylight
may permit it to disguise itself, a sufficiently powerful beam
causes the air in which the dust is suspended to appear as a
semi-solid rather than as a gas. Nobody could, in the first
instance, without repugnance place the mouth at the illuminated
focus of the electric beam and inhale the dirt revealed there. Nor
is the disgust abolished by the reflection that, although we do not
see the nastiness, we are churning it in our lungs every hour and
minute of our lives. There is no respite to this contact with dirt;
and the wonder is, not that we should from time to time suffer from
its presence, but that so small a portion of it would appear to be
deadly to man.

And what is this portion? It was some time ago the current belief
that epidemic diseases generally were propagated by a kind of
malaria, which consisted of organic matter in a state of
_motor-decay_; that when such matter was taken into the body through
the lungs or skin, it had the power of spreading there the
destroying process which had attacked itself. Such a spreading power
was visibly exerted in the case of yeast. A little leaven was seen
to leaven the whole lump, a mere speck of matter in this supposed
state of decomposition being apparently competent to propagate
indefinitely its own decay. Why should not a bit of rotten malaria
work in a similar manner within the human frame? In 1836 a very
wonderful reply was given to this question. In that year Cagniard de
la Tour discovered the _yeast plant_, a living organism, which, when
placed in a proper medium, feeds, grows, and reproduces itself, and
in this way carries on the process which we name fermentation.
Fermentation was thus proved to be a product of life instead of a
process of decay.

Schwann, of Berlin, discovered the yeast plant independently, and in
February, 1837, he also announced the important result, that when a
decoction of meat is effectually screened from ordinary air, and
supplied solely with air which has been raised to a high
temperature, putrefaction never sets in. Putrefaction, therefore, he
affirmed to be caused by something derived from the air, which
something could be destroyed by a sufficiently high temperature. The
experiments of Schwann were repeated and confirmed by Helmholtz and
Ure. But as regards fermentation, the minds of chemists, influenced
probably by the great authority of Gay-Lussac, who ascribed
putrefaction to the action of oxygen, fell back upon the old notion
of matter in a state of decay. It was not the living yeast plant,
but the dead or dying parts of it, which, assailed by oxygen,
produced the fermentation. This notion was finally exploded by
Pasteur. He proved that the so-called “ferments” are not such; that
the true ferments are organized beings which find in the reputed
ferments their necessary food.

Side by side with these researches and discoveries, and fortified by
them and others, has run the _germ theory_ of epidemic disease. The
notion was expressed by Kircher, and favored by Linnæus, that
epidemic diseases are due to germs which float in the atmosphere,
enter the body, and produce disturbance by the development within
the body of parasitic life. While it was still struggling against
great odds, this theory found an expounder and a defender in the
President of this Institution. At a time when most of his medical
brethren considered it a wild dream, Sir Henry Holland contended
that some form of the germ theory was probably true. The strength of
this theory consists in the perfect parallelism of the phenomena of
contagious disease with those of life. As a planted acorn gives
birth to an oak competent to produce a whole crop of acorns, each
gifted with the power of reproducing its parent tree, and as thus
from a single seedling a whole forest may spring, so these epidemic
diseases literally plant their seeds, grow, and shake abroad new
germs, which, meeting in the human body their proper food and
temperature, finally take possession of whole populations. Thus
Asiatic cholera, beginning in a small way in the Delta of the
Ganges, contrived in seventeen years to spread itself over nearly
the whole habitable world. The development from an infinitesimal
speck of the virus of small-pox of a crop of pustules, each charged
with the original poison, is another illustration. The reappearance
of the scourge, as in the case of the _Dreadnought_ at Greenwich,
reported on so ably by Dr. Budd and Mr. Busk, receives a
satisfactory explanation from the theory which ascribes it to the
lingering of germs about the infected place.

Surgeons have long known the danger of permitting air to enter an
open abscess. To prevent its entrance they employ a tube called a
cannula, to which is attached a sharp steel point called a trocar.
They puncture with the steel point, and by gentle pressure they
force the pus through the cannula. It is necessary to be very
careful in cleansing the instrument; and it is difficult to see how
it can be cleansed by ordinary methods in air loaded with organic
impurities, as we have proved our air to be. The instrument ought,
in fact, to be made as hot as its temper will bear. But this is not
done, and hence, notwithstanding all the surgeon’s care,
inflammation often sets in after the first operation, rendering
necessary a second and a third. Rapid putrefaction is found to
accompany this new inflammation. The pus, moreover, which was sweet
at first, and showed no trace of animal life, is now fetid, and
swarming with active little organisms called vibrios. Prof. Lister,
from whose recent lecture this fact is derived, contends, with every
show of reason, that this rapid putrefaction and this astounding
development of animal life are due to the entry of germs into the
abscess during the first operation, and their subsequent nurture and
development under favorable conditions of food and temperature. The
celebrated physiologist and physicist, Helmholtz, is attacked
annually by hay-fever. From the 20th of May to the end of June he
suffers from a catarrh of the upper air-passages; and he has found
during this period, and at no other, that his nasal secretions are
peopled by these vibrios. They appear to nestle by preference in the
cavities and recesses of the nose, for a strong sneeze is necessary
to dislodge them.

These statements sound uncomfortable; but by disclosing our enemy
they enable us to fight him. When he clearly eyes his quarry the
eagle’s strength is doubled, and his swoop is rendered sure. If the
germ theory be proved true, it will give a definiteness to our
efforts to stamp out disease which they could not previously
possess. And it is only by definite effort under its guidance that
its truth or falsehood can be established. It is difficult for an
outsider like myself to read without sympathetic emotion such papers
as those of Dr. Budd, of Bristol, on cholera, scarlet-fever, and
small-pox. He is a man of strong imagination, and may occasionally
take a flight beyond his facts; but without this dynamic heat of
heart, the stolid inertia of the free-born Briton cannot be
overcome. And as long as the heat is employed to warm up the truth
without singeing it overmuch; as long as this enthusiasm can
overmatch its mistakes by unequivocal examples of success, so long
am I disposed to give it a fair field to work in, and to wish it God
speed.

But let us return to our dust. It is needless to remark that it
cannot be blown away by an ordinary bellows; or, more correctly, the
place of the particles blown away is in this case supplied by others
ejected from the bellows, so that the track of the beam remains
unimpaired. But if the nozzle of a good bellows be filled with
cotton wool not too tightly packed, the air urged through the wool
is filtered of its floating matter, and it then forms a clean band
of darkness in the illuminated dust. This was the filter used by
Schroëder in his experiments on spontaneous generation, and turned
subsequently to account in the excellent researches of Pasteur.
Since 1868 I have constantly employed it myself.

But by far the most interesting and important illustration of this
filtering process is furnished by the human breath. I fill my lungs
with ordinary air and breathe through a glass tube across the
electric beam. The condensation of the aqueous vapor of the breath
is shown by the formation of a luminous white cloud of delicate
texture. It is necessary to abolish this cloud, and this may be done
by drying the breath previous to its entering into the beam; or
still more simply, by warming the glass tube. When this is done the
luminous track of the beam is for a time uninterrupted. The breath
impresses upon the floating matter a transverse motion, but the dust
from the lungs makes good the particles displaced. But after some
time an obscure disc appears upon the beam, the darkness of which
increases, until finally, towards the end of the expiration, the
beam is, as it were, pierced by an intensely black hole, in which no
particles whatever can be discerned. The air, in fact, has so lodged
its dirt within the lungs as to render the last portions of the
expired breath absolutely free from suspended matter. This
experiment may be repeated any number of times with the same result.
It renders the distribution of the dirt within the lungs as manifest
as if the chest were transparent.

I now empty my lungs as perfectly as possible, and placing a handful
of cotton wool against my mouth and nostrils, inhale through it.
There is no difficulty in thus filling the lungs with air. On
expiring this air through the glass tube, its freedom from floating
matter is at once manifest. From the very beginning of the act of
expiration the beam is pierced by a black aperture. The first puff
from the lungs abolishes the illuminated dust and puts a patch of
darkness in its place, and the darkness continues throughout the
entire course of the expiration. When the tube is placed below the
beam and moved to and fro, the same smoke-like appearance as that
obtained with a flame is observed. In short, the cotton wool, when
used in sufficient quantity, completely intercepts the floating
matter on its way to the lungs.

And here we have revealed to us the true philosophy of a practice
followed by medical men, more from instinct than from actual
knowledge. In a contagious atmosphere the physician places a
handkerchief to his mouth and inhales through it. In doing so he
unconsciously holds back the dirt and germs of the air. If the
poison were a gas it would not be thus intercepted. On showing this
experiment with the cotton wool to Dr. Bence Jones, he immediately
repeated it with a silk handkerchief. The result was substantially
the same, though, as might be expected, the wool is by far the
surest filter. The application of these experiments is obvious. If a
physician wishes to hold back from the lungs of his patient, or from
his own, the germs by which contagious disease is said to be
propagated, he will employ a cotton wool respirator. After the
revelations of this evening, such respirators must, I think, come
into general use as a defence against contagion. In the crowded
dwellings of the London poor, where the isolation of the sick is
difficult, if not impossible, the noxious air around the patient
may, by this simple means, be restored to practical purity. Thus
filtered, attendants may breathe the air unharmed. In all
probability the protection of the lungs will be protection of the
entire system. For it is exceedingly probable that the germs which
lodge in the air-passages, and which, at their leisure, can work
their way across the mucous membrane, are those which sow in the
body epidemic disease. If this be so, then disease can certainly be
warded off by filters of cotton wool. I should be most willing to
test their efficacy in my own person. And time will decide whether
in lung diseases also the woolen respirator cannot abate irritation,
if not arrest decay. By its means, so far as the germs are
concerned, the air of the highest Alps may be brought into the
chamber of the invalid.

III.

Scientific Use of the Imagination.

I carried with me to the Alps this year the heavy burden of this
evening’s work. In the way of new investigation I had nothing
complete enough to be brought before you; so all that remained to me
was to fall back upon such residues as I could find in the depths of
consciousness, and out of them to spin the fiber and weave the web
of this discourse. Save from memory I had no direct aid upon the
mountains; but to spur up the emotions, on which so much depends, as
well as to nourish indirectly the intellect and will, I took with me
two volumes of poetry, Goethe’s “Farbenlehre,” and the work on
“Logic” recently published by Mr. Alexander Bain. The spur, I am
sorry to say, was no match for the integument of dullness it had to
pierce.

In Goethe, so glorious otherwise, I chiefly noticed the
self-inflicted hurts of genius, as it broke itself in vain against
the philosophy of Newton. For a time Mr. Bain became my principal
companion. I found him learned and practical, shining generally with
a dry light, but exhibiting at times a flush of emotional strength,
which proved that even logicians share the common fire of humanity.
He interested me most when he became the mirror of my own condition.
Neither intellectually nor socially is it good for man to be alone,
and the griefs of thought are more patiently borne when we find that
they have been experienced by another. From certain passages in his
book I could infer that Mr. Bain was no stranger to such sorrows.
Take this passage as an illustration. Speaking of the ebb of
intellectual force which we all from time to time experience, Mr.
Bain says: “The uncertainty where to look for the next opening of
discovery brings the pain of conflict and the debility of
indecision.” These words have in them the true ring of personal
experience.

The action of the investigator is periodic. He grapples with a
subject of inquiry, wrestles with it, overcomes it, exhausts, it may
be, both himself and it for the time being. He breathes a space, and
then renews the struggle in another field. Now this period of
halting between two investigations is not always one of pure repose.
It is often a period of doubt and discomfort, of gloom and ennui.
“The uncertainty where to look for the next opening of discovery
brings the pain of conflict and the debility of indecision.” Such
was my precise condition in the Alps this year; in a score of words
Mr. Bain has here sketched my mental diagnosis; and it was under
these evil circumstances that I had to equip myself for the hour and
the ordeal that are now come.

Gladly, however, as I should have seen this duty in other hands, I
could by no means shrink from it. Disloyalty would have been worse
than failure. In some fashion or other—feebly or strongly, meanly or
manfully, on the higher levels of thought, or on the flats of
commonplace—the task had to be accomplished. I looked in various
directions for help and furtherance; but without me for a time I saw
only “antres vast,” and within me “deserts idle.” My case resembled
that of a sick doctor who had forgotten his art, and sorely needed
the prescription of a friend. Mr. Bain wrote one for me. He said:
“Your present knowledge must forge the links of connection between
what has been already achieved and what is now required.”

In these words he admonished me to review the past and recover from
it the broken ends of former investigations. I tried to do so.
Previous to going to Switzerland I had been thinking much of light
and heat, of magnetism and electricity, of organic germs, atoms,
molecules, spontaneous generation, comets and skies. With one or
another of these I now sought to re-form an alliance, and finally
succeeded in establishing a kind of cohesion between thought and
light. The wish grew within me to trace, and to enable you to trace,
some of the more occult operations of this agent. I wished, if
possible, to take you behind the drop-scene of the senses, and to
show you the hidden mechanism of optical action. For I take it to be
well worth the while of the scientific teacher to take some pains,
and even great pains, to make those whom he addresses co-partners of
his thoughts. To clear his own mind in the first place from all haze
and vagueness, and then to project into language which shall leave
no mistake as to his meaning—which shall leave even his errors
naked—the definite ideas he has shaped.

A great deal is, I think, possible to scientific exposition
conducted in this way. It is possible, I believe, even before an
audience like the present, to uncover to some extent the unseen
things of nature, and thus to give, not only to professed students,
but to others with the necessary bias, industry and capacity, an
intelligent interest in the operations of science. Time and labor
are necessary to this result, but science is the gainer from the
public sympathy thus created.

How then are those hidden things to be revealed? How, for example,
are we to lay hold of the physical basis of light, since, like that
of life itself, it lies entirely without the domain of the senses?
Now, philosophers may be right in affirming that we cannot transcend
experience. But we can, at all events, carry it a long way from its
origin. We can also magnify, diminish, qualify, and combine
experiences, so as to render them fit for purposes entirely new. We
are gifted with the power of imagination, combining what the Germans
called _Anschauungsgabe_ and _Einbildungskraft_, and by this power
we can lighten the darkness which surrounds the world of the senses.

There are tories even in science who regard imagination as a faculty
to be feared and avoided rather than employed. They had observed its
action in weak vessels and were unduly impressed by its disasters.
But they might with equal justice point to exploded boilers as an
argument against the use of steam. Bounded and conditioned by
coöperant reason, imagination becomes the mightiest instrument of
the physical discoverer. Newton’s passage from a falling apple to a
falling moon was a leap of the imagination. When William Thomson
tries to place the ultimate particles of matter between his compass
points, and to apply to them a scale of millimeters, it is an
exercise of the imagination. And in much that has been recently said
about protoplasm and life, we have the outgoings of the imagination
guided and controlled by the known analogies of science. In fact,
without this power our knowledge of nature would be a mere
tabulation of coëxistences and sequences. We should still believe in
the succession of day and night, of summer and winter; but the soul
of force would be dislodged from our universe; casual relations
would disappear, and with them that science which is now binding the
parts of nature to an organic whole.

I should like to illustrate by a few simple instances the use that
scientific men have already made of this power of imagination, and
to indicate afterwards some of the further uses that they are likely
to make of it. Let us begin with the rudimentary experiences.
Observe the falling of heavy rain drops into a tranquil pond. Each
drop as it strikes the water becomes a center of disturbance, from
which a series of ring ripples expands outwards. Gravity and inertia
are the agents by which this wave motion is produced, and a rough
experiment will suffice to show that the rate of propagation does
not amount to a foot a second.

A series of slight mechanical shocks is experienced by a body
plunged in the water as the wavelets reach it in succession. But a
finer motion is at the same time set up and propagated. If the head
and ears be immersed in the water, as in an experiment of
Franklin’s, the shock of the drop is communicated to the auditory
nerve—the _tick_ of the drop is heard. Now this sonorous impulse is
propagated, not at the rate of a foot a second, but at the rate of
4,700 feet a second. In this case it is not the gravity but the
_elasticity_ of the water that is the urging force. Every liquid
particle pushed against its neighbor delivers up its motion with
extreme rapidity, and the pulse is propagated as a thrill. The
incompressibility of water, as illustrated by the famous Florentine
experiment, is a measure of its elasticity, and to the possession of
this property in so high a degree the rapid transmission of a
sound-pulse through water is to be ascribed.

But water, as you know, is not necessary to the conduction of sound;
air is its most common vehicle. And you know that when the air
possesses the particular density and elasticity corresponding to the
temperature of freezing water, the velocity of sound in it is 1,090
feet a second. It is almost exactly one-fourth of the velocity in
water; the reason being that though the greater weight of the water
tends to diminish the velocity, the enormous molecular elasticity of
the liquid far more than atones for the disadvantage due to weight.
By various contrivances we can compel the vibrations of the air to
declare themselves; we know the length and frequency of sonorous
waves, and we have also obtained great mastery over the various
methods by which the air is thrown into vibration. We know the
phenomena and laws of vibrating rods, of organ pipes, strings,
membranes, plates, and bells. We can abolish one sound by another.
We know the physical meaning of music and noise, of harmony and
discord. In short, as regards sound we have a very clear notion of
the external physical processes which correspond to our sensations.

In these phenomena of sound we travel a very little way from
downright sensible experience. Still the imagination is to some
extent exercised. The bodily eye, for example, cannot see the
condensations and rarefactions of the waves of sound. We construct
them in thought, and we believe as firmly in their existence as in
that of the air itself. But now our experience has to be carried
into a new region, where a new use is to be made of it.

Having mastered the cause and mechanism of sound, we desire to know
the cause and mechanism of light. We wish to extend our inquiries
from the auditory nerve to the optic nerve. Now there is in the
human intellect a power of expansion—I might almost call it a power
of creation—which is brought into play by the simple brooding upon
facts. The legend of the Spirit brooding over chaos may have
originated in a knowledge of this power. In the case now before us
it has manifested itself by transplanting into space, for the
purposes of light, an adequately modified form of the mechanism of
sound. We know intimately whereon the velocity of sound depends.
When we lessen the density of a medium and preserve its elasticity
constant, we augment the velocity. When we highten the elasticity
and keep the density constant, we also augment the velocity. A small
density, therefore, and a great elasticity are the two things
necessary to rapid propagation.

Now light is known to move with the astounding velocity of 185,000
miles a second. How is such a velocity to be obtained? By boldly
diffusing in space a medium of the requisite tenuity and elasticity.
Let us make such a medium our starting point, endowing it with one
or two other necessary qualities; let us handle it in accordance
with strict mechanical laws; give to every step of your deduction
the surety of the syllogism; carry it thus forth from the world of
imagination to the world of sense, and see whether the final outcrop
of the deduction be not the very phenomena of light which ordinary
knowledge and skilled experiment reveal. If in all the multiplied
varieties of these phenomena, including those of the most remote and
entangled description, this fundamental conception always brings us
face to face with the truth; if no contradiction to our deductions
from it be found in external nature; if, moreover, it has actually
forced upon our attention phenomena which no eye had previously
seen, and which no mind had previously imagined; if by it we are
gifted with a power of prescience which has never failed when
brought to an experimental test; such a conception, which never
disappoints us, but always lands us on the solid shores of fact,
must, we think, be something more than a mere figment of the
scientific fancy. In forming it that composite and creative unity in
which reason and imagination are together blent, has, we believe,
led us into a world not less real than that of the senses, and of
which the world of sense itself is the suggestion and justification.

Far be it from me, however, to wish to fix you immovably in this or
in any other theoretic conception. With all our belief of it, it
will be well to keep the theory plastic and capable of change. You
may, moreover, urge that although the phenomena occur _as if_ the
medium existed, the absolute demonstration of its existence is still
wanting. Far be it from me to deny to this reasoning such validity
as it may fairly claim. Let us endeavor by means of analogy to form
a fair estimate of its force.

You believe that in society you are surrounded by reasonable beings
like yourself. You are, perhaps, as firmly convinced of this as of
anything. What is your warrant for this conviction? Simply and
solely this, your fellow-creatures behave as if they were
reasonable; the hypothesis, for it is nothing more, accounts for the
facts. To take an eminent example, you believe that our president is
a reasonable being. Why? There is no known method of superposition
by which any one of us can apply himself intellectually to another
so as to demonstrate coincidence as regards the possession of
reason. If, therefore, you hold our president to be reasonable, it
is because he behaves _as if_ he were reasonable. As in the case of
the ether, beyond the “_as if_” you cannot go. Nay, I should not
wonder if a close comparison of the data on which both inferences
rest caused many respectable persons to conclude that the ether had
the best of it.

This universal medium, this light-ether as it is called, is a
vehicle, not an origin of wave motion. It receives and transmits,
but it does not create. Whence does it derive the motions it
conveys? For the most part from luminous bodies. By this motion of a
luminous body I do not mean its sensible motion, such as the flicker
of a candle, or the shooting out of red prominences from the limb of
the sun. I mean an intestine motion of the atoms or molecules of the
luminous body. But here a certain reserve is necessary. Many
chemists of the present day refuse to speak of atoms and molecules
as real things. Their caution leads them to stop short of the clear,
sharp, mechanically intelligible atomic theory enunciated by Dalton,
or any form of that theory, and to make the doctrine of multiple
proportions their intellectual bourne. I respect the caution, though
I think it is here misplaced. The chemists who recoil from these
notions of atoms and molecules accept without hesitation the
undulatory theory of light. Like you and me they one and all believe
in an ether and its light-producing waves. Let us consider what this
belief involves.

Bring your imaginations once more into play and figure a series of
sound waves passing through air. Follow them up to their origin, and
what do you there find? A definite, tangible, vibrating body. It may
be the vocal chords of a human being, it may be an organ pipe, or it
may be a stretched string. Follow in the same manner a train of
ether waves to their source, remembering at the same time that your
ether is matter, dense, elastic, and capable of motions subject to
and determined by mechanical laws. What then do you expect to find
as the source of a series of ether waves? Ask your imagination if it
will accept a vibrating multiple proportion—a numerical ratio in a
state of oscillation? I do not think it will. You cannot crown the
edifice by this abstraction. The scientific imagination, which is
here authoritative, demands as the origin and cause of a series of
ether waves a particle of vibrating matter quite as definite, though
it may be excessively minute, as that which gives origin to a
musical sound. Such a particle we name an atom or a molecule. I
think the imagination when focused so as to give definition without
penumbral haze is sure to realize this image at last.

To preserve thought continuous throughout this discourse, to prevent
either lack of knowledge or failure of memory from producing any
rent in our picture, I here propose to run rapidly over a bit of
ground which is probably familiar to most of you, but which I am
anxious to make familiar to you all.

The waves generated in the ether by the swinging atoms of luminous
bodies are of different lengths and amplitudes. The amplitude is the
width of swing of the individual particles of the wave. In water
waves it is the hight of the crest above the trough, while the
length of the wave is the distance between two consecutive crests.
The aggregate of waves emitted by the sun may be broadly divided
into two classes, the one class competent, the other incompetent, to
excite vision.

But the light-producing waves differ markedly among themselves in
size, form, and force. The length of the largest of these waves is
about twice that of the smallest, but the amplitude of the largest
is probably a hundred times that of the smallest. Now the force or
energy of the wave, which, expressed with reference to sensation,
means the intensity of the light, is proportional to the square of
the amplitude. Hence the amplitude being one hundred-fold, the
energy of the largest light-giving waves would be ten thousand-fold
that of the smallest. This is not improbable. I use these figures,
not with a view to numerical accuracy, but to give you definite
ideas of the differences that probably exist among the light-giving
waves. And if we take the whole range of solar radiation into
account—its non-visual as well as its visual waves—I think it
probable that the force or energy of the largest wave is a million
times that of the smallest.

Turned into their equivalents of sensation, the different light
waves produce different colors. Red, for example, is produced by the
largest waves, violet by the smallest, while green is produced by a
wave of intermediate length and amplitude. On entering from air into
more highly refracting substances, such as glass or water or the
sulphide of carbon, all the waves are retarded, but the smallest
ones most. This furnishes a means of separating the different
classes of waves from each other—in other words, of analyzing the
light. Sent through a refracting prism, the waves of the sun are
turned aside in different degrees from their direct course, the red
least, the violet most. They are virtually pulled asunder, and they
paint upon a white screen placed to receive them “the solar
spectrum.”

Strictly speaking, the spectrum embraces an infinity of colors, but
the limits of language and of our powers of distinction cause it to
be divided into seven segments: Red, orange, yellow, green, blue,
indigo, violet. These are the seven primary or prismatic colors.
Separately, or mixed in various proportions, the solar waves yield
all the colors observed in nature and employed in art. Collectively
they give us the impression of whiteness. Pure unsifted solar light
is white; and if all the wave constituents of such light be reduced
in the same proportion, the light, though diminished in intensity,
will still be white. The whiteness of Alpine snow with the sun
shining upon it is barely tolerable to the eye. The same snow under
an overcast firmament is still white. Such a firmament enfeebles the
light by reflection, and when we lift ourselves above a
cloud-field—to an Alpine summit, for instance, or to the top of
Snowdon—and see, in the proper direction, the sun shining on the
clouds, they appear dazzlingly white. Ordinary clouds, in fact,
divide the solar light impinging on them into two parts—a reflected
part and a transmitted part, in each of which the proportions of
wave motion which produce the impression of whiteness are sensibly
preserved.