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.