The water analogy was again called into play in the shape of a model
for the better demonstration of the problem. The defects in existing
electric machines and the means of increasing the E.M.F. were discussed,
the conclusions pointing to the future use of very large machines and
very high velocities. The future of telephonic communication received a
passing remark, and attention called to the future of electric railways.
The small experiments of Siemens have determined the ultimate success of
this kind of railway. Their introduction is merely a question of time
and capital. The first cost of electric railways would be smaller than
that of steam railways; the working expenses would also be reduced.
The rails would be lighter, the rolling stock lighter, the bridges and
viaducts less costly, and in the underground railways the atmosphere
would not be vitiated.
"About two years ago, it struck Professor Ayrton and myself, when
thinking how very faint musical sounds are heard distinctly from the
telephone, in spite of loud noises in the neighborhood, that there
was an application of this principle of recurrent effects of far more
practical importance than any other, namely, in the use of musical notes
for coast warnings in thick weather. You will say that fog bells and
horns are an old story, and that they have not been particularly
successful, since in some states of the weather they are audible, in
others not.
"Now, it seems to be forgotten by everybody that there is a medium of
communicating with a distant ship, namely, the water, which is not at
all influenced by changes in the weather. At some twenty or thirty feet
below the surface there is exceedingly little disturbance of the water,
although there may be large waves at the surface. Suppose a large
water-siren like this--experiment shown--is working at as great a depth
as is available, off a dangerous coast, the sound it gives out is
transmitted so as to be heard at exceedingly great distances by an ear
pressed against a strip of wood or metal dipping into the water. If the
strip is connected with a much larger wooden or metallic surface in the
water the sound is heard much more distinctly. Now, the sides of a ship
form a very large collecting surface, and at the distance of several
miles from such a water siren as might be constructed, we feel quite
sure that, above the noise of engines and flapping sails, above the far
more troublesome noise of waves striking the ship's side, the musical
note of the distant siren would be heard, giving warning of a dangerous
neighborhood. In considering this problem, you must remember that
Messrs. Colladon and Sturn heard distinctly the sound of a bell struck
underwater at the distance of nearly nine miles, the sound being
communicated by the water of Lake Geneva."
The next portion of the lecture discussed the great value of a rapid
recurrence of effects, the obtaining of sound by means of a rapid
intermission of light rays on selenium joined up in an electric circuit
being instanced as an example. Then recent experiments on the refractive
power of ebonite were detailed--the rough results tending to give
greater weight to Clerk-Maxwell's electro-magnetic theory of light. The
index of refraction of ebonite was found by Profs. Ayrton and Perry to
be roughly 1.7. Clerk-Maxwell's theory requires that the square of this
number should be equal to the electric specific inductive capacity of
the substance. For ebonite this electric constant varies from 2.2 to 3.5
for different specimens, the mean of which is almost exactly equal to
the square of 1.7.
* * * * *
RESEARCHES ON THE RADIANT MATTER OF CROOKES AND THE MECHANICAL THEORY OF
ELECTRICITY.
By DR. W. F. GINTL, abstracted by DR. VON GERICHTEN.
The author discusses the question whether, according to the experiments
of Crookes, the assumption of an especial fourth state of aggregation is
necessary, or whether the facts may be satisfactorily explained without
such hypothesis? He shows that the latter alternative is possible with
the aid of a mechanical theory of electricity. If the radiant matter
produced in the vacuum is a phenomenon _sui generis,_ produced by the
action of electricity and heat upon the molecules of gas remaining in
the receiver, it is, in the first place, doubtful to apply to it the
conception of an aggregate condition. The author considers it impossible
to form a clear understanding of the phenomena in accordance with the
theory of Crookes, or to find in the facts any evidence of the existence
of radiant matter. An explanation of the latter phenomenon is thus
given: Particles become separated from the surface of the substance of
the negative pole, they are repelled, and they move away from the pole
with a speed resulting from the antagonistic forces in a parallel and
rectilinear direction, preserving their speed and their initial path so
long as they do not meet with obstacles which influence their movement.
At a certain density of the gases present in the exhausted space, these
particles, in consequence of the impact of gaseous molecules more or
less opposed to their direction of movement, lose their velocity after
traveling a short distance and soon come to rest. The more dilute the
gas the smaller is the number of the impacts of the gaseous molecules
encountering the molecules of the poles, and at a certain degree of
dilution the repelled polar particles will be able to traverse the space
open to them without any essential alteration in their speed, the small
number of the existing gaseous molecules being no longer able to retard
the molecules of the polar no their journey through the apparatus. The
luminous phenomena of the Geissler tubes the author supposes to be
produced by the intense blows which the gaseous molecules receive from
the polar molecules flying rapidly through the apparatus. The intensity
of the luminous phenomena will naturally decrease with the number of
the photophorous particles occupying the space. Accordingly in the
experiments of Crookes, on continued rarefaction of the gas, a condition
was reached where a display of light is no longer perceptible, or can be
made visible merely by the aid of fluorescent bodies. A condition may
also appear, as is shown by Crookes' experiment, with the metallic plate
intercalated as negative pole in the middle of. a Geissler tube, with
the positive poles at the ends. In this case the gaseous molecules are,
so to speak, driven away by the polar particles endowed with an equal
initial velocity, till at a certain distance from the pole the mass of
the gaseous molecules and their speed become so great that a luminous
display begins. In an analogous manner the author explains the phenomena
of phosphorescence which Crookes' elicits by the action of his radiant
matter. In like manner the thermic and the mechanical effects are most
simply explained, according to the expression selected by Crookes
himself, as the results of a "continued molecular bombardment." The
attraction of the so called radiant matter, regarded as a stream of
metallic particles by the magnet, will not appear surprising.
* * * * *