from its publication, yet the critical process which his views undergo
is extremely helpful to the subject-matter of them. All the defects
which necessarily adhere to the new view are gradually discovered and
eliminated. Over-rating and exaggeration give way to more sober
estimates. And so it came about that it was found unpermissible to
attribute all functions of orientation exclusively to the labyrinth. In
these critical labors Delage, Aubert, Breuer, Ewald, and others have
rendered distinguished services. It can also not fail to happen that
fresh facts become known in this process which could have been predicted
by the new view, which actually were predicted in part, and which
consequently furnish a support for the new view. Breuer and Ewald
succeeded in electrically and mechanically exciting the labyrinth, and
even single parts of the labyrinth, and thus in producing the movements
that belong to such stimuli. It was shown that when the semi-circular
canals were absent vertigo could not be produced, when the entire
labyrinth was removed the orientation of the head was no longer
possible, that without the labyrinth galvanic vertigo could not be
induced. I myself constructed as early as 1875 an apparatus for
observing animals in rotation, which was subsequently reinvented in
various forms and has since received the name of "cyclostat."[103] In
experiments with the most varied kinds of animals it was shown that, for
example, the larvæ of frogs are not subject to vertigo until their
semi-circular canals which at the start are wanting are developed (K.
Schäfer). A large percentage of the deaf and dumb are afflicted with
grave affections of the labyrinth. The American psychologist, William
James, has made whirling experiments with many deaf and dumb subjects,
and in a large number of them found that susceptibility to giddiness is
wanting. He also found that many deaf and dumb people on being ducked
under water, whereby they lose their weight and consequently have no
longer the full assistance of their muscular sense, utterly lose their
sense of position in space, do not know which is up and which is down,
and are thrown into the greatest consternation,--results which do not
occur in normal men. Such facts are convincing proof that we do not
orientate ourselves entirely by means of the labyrinth, important as it
is for us. Dr. Kreidl has made experiments similar to those of James and
found that not only is vertigo absent in deaf and dumb people when
whirled about, but that also the reflex movements of the eyes which are
normally induced by the labyrinth are wanting. Finally, Dr. Pollak has
found that galvanic vertigo does not exist in a large percentage of the
deaf and dumb. Neither the jerking movements nor the uniform movements
of the eyes were observed which normal human beings exhibit in the
Ritter and Purkinje experiment.
After the physicist has arrived at the idea that the semi-circular
canals are the organ of sensation of rotation or of angular
acceleration, he is next constrained to ask for the organs that mediate
the sensation of acceleration noticed in forward movements. In
searching for an organ for this function, he of course is not apt to
select one that stands in no anatomical and spatial relation with the
semi-circular canals. And in addition there are physiological
considerations to be weighed. The preconceived opinion once having been
abandoned that the _entire_ labyrinth is auditory in its function, there
remains after the cochlea is reserved for sensations of tone and the
semi-circular canals for the sensation of angular acceleration, the
vestibule for the discharge of additional functions. The vestibule,
particularly the part of it known as the sacculus, appeared to me, by
reason of the so-called otoliths which it contains, eminently adapted
for being the organ of sensation of forward acceleration or of the
position of the head. In this conjecture I again closely coincided with
Breuer.
That a sensation of position, of direction and amount of
mass-acceleration exists, our experience in elevators as well as of
movement in curved paths is sufficient proof. I have also attempted to
produce and destroy suddenly great velocities of forward movement by
means of various contrivances of which I shall mention only one here.
If, while enclosed in the paper box of my large whirling apparatus at
some distance from the axis, my body is in uniform rotation which I no
longer feel, and I then loosen the connexions of the frame _rr_ with _R_
thus making the former moveable and I then suddenly stop the larger
frame, my forward motion is abruptly impeded while the frame _rr_
continues to rotate. I imagine now that I am speeding on in a straight
line in a direction opposite to that of the checked motion.
Unfortunately, for many reasons it cannot be proved convincingly that
the organ in question has its seat in the head. According to the opinion
of Delage, the labyrinth has nothing to do with this particular
sensation of movement. Breuer, on the other hand, is of the opinion that
the organ of forward movement in man is stunted and the persistence of
the sensation in question is too brief to permit our instituting
experiments as obvious as in the case of rotation. In fact, Crum Brown
once observed while in an irritated condition peculiar vertical
phenomena in his own person, which were all satisfactorily explained by
an abnormally long persistence of the sensation of rotation, and I
myself in an analogous case on the stopping of a railway train felt the
apparent backward motion in striking intensity and for an unusual length
of time.
There is no doubt whatever that we feel changes of vertical
acceleration, and it will appear from the following extremely probable
that the otoliths of the vestibule are the sense-organ for the
_direction_ of the mass-acceleration. It will then be incompatible with
a really logical view to regard the latter as incapable of sensing
horizontal accelerations.
In the lower animals the analogue of the labyrinth is shrunk to a little
vesicle filled with a liquid and containing tiny crystals, auditive
stones, or otoliths, of greater specific gravity, suspended on minute
hairs. These crystals appear physically well adapted for indicating both
the direction of gravity and the direction of incipient movements. That
they discharge the former function, Delage was the first to convince
himself by experiments with lower animals which on the removal of the
otoliths utterly lost their bearings and could no longer regain their
normal position. Loeb also found that fishes without labyrinths swim now
on their bellies and now on their backs. But the most remarkable, most
beautiful, and most convincing experiment is that which Dr. Kreidl
instituted with crustaceans. According to Hensen, certain Crustacea on
sloughing spontaneously introduce fine grains of sand as auditive stones
into their otolith vesicle. At the ingenious suggestion of S. Exner, Dr.
Kreidl constrained some of these animals to put up with iron filings
(_ferrum limatum_). If the pole of an electro-magnet be brought near the
animal, it will at once turn its back away from the pole accompanying
the movement with appropriate reflex motions of the eye the moment the
current is closed, exactly as if gravity had been brought to bear upon
the animal in the same direction as the magnetic force.[104] This, in
fact, is what should be expected from the function ascribed to the
otoliths. If the eyes be covered with asphalt varnish, and the auditive
sacs removed, the crustaceans lose their sense of direction utterly,
tumble head over heels, lie on their side or their back indifferently.
This does not happen when the eyes only are covered. For vertebrates,
Breuer has demonstrated by searching investigations that the otoliths,
or better, statoliths, slide in three planes parallel to the planes of
the semi-circular canals, and are consequently perfectly adapted for
indicating changes both in the amount and the direction of the
mass-acceleration.[105]
I have already remarked that not every function of orientation can be
ascribed exclusively to the labyrinth. The deaf and dumb who have to be
immersed in water, and the crustaceans who must have their eyes closed
if they are to be perfectly disorientated, are proof of this fact. I saw
a blind cat at Hering's laboratory which to one who was not a very
attentive observer behaved exactly like a seeing cat. It played nimbly
with objects rolling on the floor, stuck its head inquisitively into
open drawers, sprang dexterously upon chairs, ran with perfect accuracy
through open doors, and never bumped against closed ones. The visual
sense had here been rapidly replaced by the tactual and auditive senses.
And it appears from Ewald's investigations that even after the
labyrinths have been removed, animals gradually learn to move about
again quite in the normal fashion, presumably because the eliminated
function of the labyrinth is now performed by some part of the brain. A
certain peculiar weakness of the muscles alone is perceptible which
Ewald ascribes to the absence of the stimulus which is otherwise
constantly emitted by the labyrinth (the labyrinth-tonus). But if the
part of the brain which discharges the deputed function be removed, the
animals are again completely disorientated and absolutely helpless.
It may be said that the views enunciated by Breuer, Crum Brown and
myself in 1873 and 1874, and which are substantially a fuller and richer
development of Goltz's idea, have upon the whole been substantiated. At
least they have exercised a helpful and stimulative influence. New
problems have of course arisen in the course of the investigation which
still await solution, and much work remains to be done. At the same time
we see how fruitful the renewed co-operation of the various special
departments of science may become after a period of isolation and
invigorating labor apart.
I may be permitted, therefore, to consider the relation between hearing
and orientation from another and more general point of view. What we
call the auditive organ is in the lower animals simply a sac containing
auditive stones. As we ascend the scale, 1, 2, 3 semi-circular canals
gradually develop from them, whilst the structure of the otolith organ
itself becomes more complicated. Finally, in the higher vertebrates, and
particularly in the mammals, a part of the latter organ (the lagena)
becomes the cochlea, which Helmholtz explained as the organ for
sensations of tone. In the belief that the entire labyrinth was an
auditive organ, Helmholtz, contrary to the results of his own masterly
analysis, originally sought to interpret another part of the labyrinth
as the organ of noises. I showed a long time ago (1873) that every tonal
stimulus by shortening the duration of the excitation to a few
vibrations, gradually loses its character of pitch and takes on that of
a sharp, dry report or noise.[106] All the intervening stages between
tones and noises can be exhibited. Such being the case, it will hardly
be assumed that one organ is suddenly and at some given point replaced
in function by another. On the basis of different experiments and
reasonings S. Exner also regards the assumption of a special organ for
the sensing of noises as unnecessary.
If we will but reflect how small a portion of the labyrinth of higher
animals is apparently in the service of the sense of hearing, and how
large, on the other hand, the portion is which very likely serves the
purposes of orientation, how much the first anatomical beginnings of the
auditive sac of lower animals resemble that part of the fully developed
labyrinth which does not hear, the view is irresistibly suggested which
Breuer and I (1874, 1875) expressed, that the auditive organ took its
development from an organ for sensing movements by adaptation to weak
periodic motional stimuli, and that many apparatuses in the lower
animals which are held to be organs of hearing are not auditive organs
at all.[107]
This view appears to be perceptibly gaining ground. Dr. Kreidl by
skilfully-planned experiments has arrived at the conclusion that even
fishes do not hear, whereas E. H. Weber, in his day, regarded the
ossicles which unite the air-bladder of fishes with the labyrinth as
organs expressly designed for conducting sound from the former to the
latter.[108] Störensen has investigated the excitation of sounds by the
air-bladder of fishes, as also the conduction of shocks through Weber's
ossicles. He regards the air-bladder as particularly adapted for
receiving the noises made by other fishes and conducting them to the
labyrinth. He has heard the loud grunting tones of the fishes in South
American rivers, and is of the opinion that they allure and find each
other in this manner. According to these views certain fishes are
neither deaf nor dumb.[109] The question here involved might be solved
perhaps by sharply distinguishing between the sensation of hearing
proper, and the perception of shocks. The first-mentioned sensation may,
even in the case of many vertebrates, be extremely restricted, or
perhaps even absolutely wanting. But besides the auditive function,
Weber's ossicles may perfectly well discharge some other function.
Although, as Moreau has shown, the air-bladder itself is not an organ of
equilibrium in the simple physical sense of Borelli, yet doubtless some
function of this character is still reserved for it. The union with the
labyrinth favors this conception, and so a host of new problems rises
here before us.
I should like to close with a reminiscence from the year 1863.
Helmholtz's _Sensations of Tone_ had just been published and the
function of the cochlea now appeared clear to the whole world. In a
private conversation which I had with a physician, the latter declared
it to be an almost hopeless undertaking to seek to fathom the function
of the other parts of the labyrinth, whereas I in youthful boldness
maintained that the question could hardly fail to be solved, and that
very soon, although of course I had then no glimmering of how it was to
be done. Ten years later the question was substantially solved.
To-day, after having tried my powers frequently and in vain on many
questions, I no longer believe that we can make short work of the
problems of science. Nevertheless, I should not consider an
"ignorabimus" as an expression of modesty, but rather as the opposite.
That expression is a suitable one only with regard to problems which are
wrongly formulated and which are therefore not problems at all. Every
real problem can and will be solved in due course of time without
supernatural divination, entirely by accurate observation and close,
searching thought.
FOOTNOTES:
[Footnote 93: A lecture delivered on February 24, 1897, before the
_Verein zur Verbreitung naturwissenschaftlicher Kenntnisse in
Wien_.]
[Footnote 94: Wollaston, _Philosophical Transactions, Royal
Society_, 1810. In the same place Wollaston also describes and
explains the creaking of the muscles. My attention was recently
called to this work by Dr. W. Pascheles.--Cf. also Purkinje, _Prager
medicin_. _Jahrbücher_, Bd. 6, Wien, 1820.]
[Footnote 95: Similarly many external forces do not act at once on
all parts of the earth, and the internal forces which produce
deformations act at first immediately only upon limited parts. If
the earth were a feeling being, the tides and other terrestrial
events would provoke in it similar sensations to those of our
movements. Perhaps the slight alterations of the altitude of the
pole which are at present being studied are connected with the
continual slight deformations of the central ellipsoid occasioned by
seismical happenings.]
[Footnote 96: For the popular explanation by unconscious inference
the matter is extremely simple. We regard the railway carriage as
vertical and unconsciously infer the inclination of the trees. Of
course the opposite conclusion that we regard the trees as vertical
and infer the inclination of the carriage, unfortunately, is equally
clear on this theory.]
[Footnote 97: It will be observed that my way of thinking and
experimenting here is related to that which led Knight to the
discovery and investigation of the geotropism of plants.
_Philosophical Transactions_, January 9, 1806. The relations between
vegetable and animal geotropism have been more recently investigated
by J. Loeb.]
[Footnote 98: This experiment is doubtless related to the
galvanotropic experiment with the larvæ of frogs described ten years
later by L. Hermann. Compare on this point my remarks in the
_Anzeiger der Wiener Akademie_, 1886, No. 21. Recent experiments in
galvanotropism are due to J. Loeb.]
[Footnote 99: _Wiener Akad._, 6 November, 1873.]
[Footnote 100: _Wiener Gesellschaft der Aerzte_, 14 November, 1874.]
[Footnote 101: I have made a contribution to this last question in
my _Analysis of the Sensations_, (1886), English translation, 1897.]
[Footnote 102: In my _Grundlinien der Lehre von den
Bewegungsempfindungen_, 1875, the matter occupying lines 4 to 13 of
page 20 from below, which rests on an error, is, as I have also
elsewhere remarked, to be stricken out. For another experiment
related to that of Foucault, compare my _Mechanics_, p. 303.]
[Footnote 103: _Anzeiger der Wiener Akad._, 30 December, 1875.]
[Footnote 104: The experiment was specially interesting for me as I
had already attempted in 1874, although with very little confidence
and without success, to excite electromagnetically my own labyrinth
through which I had caused a current to pass.]
[Footnote 105: Perhaps the discussion concerning the peculiarity of
cats always falling on their feet, which occupied the Parisian
Academy, and, incidentally, Parisian society a few years ago, will
be remembered here. I believe that the questions which arose are
disposed of by the considerations advanced in my
_Bewegungsempfindungen_ (1875). I also partly gave, as early as
1866, the apparatus conceived by the Parisian scientists to
illustrate the phenomena in question. One difficulty was left
untouched in the Parisian debate. The otolith apparatus of the cat
can render it no service in _free_ descent. The cat, however, while
at rest, doubtless knows its position in space and is instinctively
conscious of the amount of movement which will put it on its feet.]
[Footnote 106: See the Appendix to the English edition of my
_Analysis of the Sensations_, Chicago, 1897.]
[Footnote 107: Compare my _Analysis of Sensations_, p. 123 ff.]
[Footnote 108: E. H. Weber, _De aure et auditu hominis et
animalium_, Lipsiae, 1820.]
[Footnote 109: Störensen, _Journ. Anat. Phys._, London, Vol. 29
(1895).]
ON SOME PHENOMENA ATTENDING THE FLIGHT OF PROJECTILES.[110]
"I have led my ragamuffins where they were peppered."--_Falstaff._
"He goes but to see a noise that he heard."--_Midsummer Night's
Dream._
To shoot, in the shortest time possible, as many holes as possible in
one another's bodies, and not always for exactly pardonable objects and
ideals, seems to have risen to the dignity of a duty with modern men,
who, by a singular inconsistency, and in subservience to a diametrically
contrary ideal, are bound by the equally holy obligation of making these
holes as small as possible, and, when made, of stopping them up and of
healing them as speedily as possible. Since, then, shooting and all that
appertains thereto, is a very important, if not the most important,
affair of modern life, you will doubtless not be averse to giving your
attention for an hour to some experiments which have been undertaken,
not for advancing the ends of war, but for promoting the ends of
science, and which throw some light on the phenomena attending the
flight of projectiles.
Modern science strives to construct its picture of the world not from
speculations but so far as possible from facts. It verifies its
constructs by recourse to observation. Every newly observed fact
completes its world-picture, and every divergence of a construct from
observation points to some imperfection, to some lacuna in it. What is
seen is put to the test of, and supplemented by, what is thought, which
is again naught but the result of things previously seen. It is always
peculiarly fascinating, therefore, to subject to direct verification by
observation, that is, to render palpable to the senses, something which
we have only theoretically excogitated or theoretically surmised.
In 1881, on hearing in Paris the lecture of the Belgian artillerist
Melsens, who hazarded the conjecture that projectiles travelling at a
high rate of speed carry masses of compressed air before them which are
instrumental in producing in bodies struck by the projectiles certain
well-known facts of the nature of explosions, the desire arose in me of
experimentally testing his conjecture and of rendering the phenomenon,
if it really existed, perceptible. The desire was the stronger as I
could say that all the means for realising it existed, and that I had in
part already used and tested them for other purposes.
And first let us get clear regarding the difficulties which have to be
surmounted. Our task is that of observing a bullet or other projectile
which is rushing through space at a velocity of many hundred yards a
second, together with the disturbances which the bullet causes in the
surrounding atmosphere. Even the opaque solid body itself, the
projectile, is only exceptionally visible under such circumstances--only
when it is of considerable size and when we see its line of flight in
strong perspective abridgement so that the velocity is apparently
diminished. We see a large projectile quite clearly when we stand behind
the cannon and look steadily along its line of flight or in the less
pleasant case when the projectile is speeding towards us. There is,
however, a very simple and effective method of observing swiftly moving
bodies with as little trouble as if they were held at rest at some point
in their path. The method is that of illumination by a brilliant
electric spark of extremely short duration in a dark room. But since,
for the full intellectual comprehension of a picture presented to the
eye, a certain, not inconsiderable interval of time is necessary, the
method of instantaneous photography will naturally also be employed. The
pictures, which are of extremely minute duration, are thus permanently
recorded and can be examined and analysed at one's convenience and
leisure.
With the difficulty just mentioned is associated still another and
greater difficulty which is due to the air. The atmosphere in its usual
condition is generally not visible even when at rest. But the task
presented to us is to render visible masses of air which in addition
are moving with a high velocity.
To be visible, a body must either emit light itself, must shine, or must
affect in some way the light which falls upon it, must take up that
light entirely or partly, absorb it, or must have a deflective effect
upon it, that is, reflect or refract it. We cannot see the air as we can
a flame, for it shines only exceptionally, as in a Geissler's tube. The
atmosphere is extremely transparent and colorless; it cannot be seen,
therefore, as a dark or colored body can, or as chlorine gas can, or
vapor of bromine or iodine. Air, finally, has so small an index of
refraction and so small a deflective influence upon light, that the
refractive effect is commonly imperceptible altogether.
A glass rod is visible in air or in water, but it is almost invisible in
a mixture of benzol and bisulphuret of carbon, which has the same mean
index of refraction as the glass. Powdered glass in the same mixture has
a vivid coloring, because owing to the decomposition of the colors the
indices are the same for only one color which traverses the mixture
unimpeded, whilst the other colors undergo repeated reflexions.[111]
Water is invisible in water, alcohol in alcohol. But if alcohol be mixed
with water the flocculent streaks of the alcohol in the water will be
seen at once and _vice versa_. And in like manner the air, too, under
favorable circumstances, may be seen. Over a roof heated by the burning
sun, a tremulous wavering of objects is noticeable, as there is also
over red-hot stoves, radiators, and registers. In all these cases tiny
flocculent masses of hot and cold air, of slightly differing
refrangibility, are mingled together.
In like manner the more highly refracting parts of non-homogeneous
masses of glass, the so-called striæ or imperfections of the glass, are
readily detectible among the less refracting parts which constitute the
bulk of the same. Such glasses are unserviceable for optical purposes,
and special attention has been devoted to the investigation of the
methods for eliminating or avoiding these defects. The result has been
the development of an extremely delicate method for detecting optical
faults--the so-called method of Foucault and Toepler--which is suitable
also for our present purpose.
[Illustration: Fig. 49.]