Evening star. [volume] (Washington, D.C.) 1854-1972, 1891-08-19

| For twenty i've years IL was taught that Light
was An elastic pulsation in an incompressible
jelly-hke medium. Some of the mathematical
| deductions Of Green he could only reconcile
with the observed phenomena by making the
| ether incompressible.
In 1865 Maxwell proposed his theory that
| light was an electric displacement in a plane at
right angles to the line Of propagation. Max
well theory met with great favor. 1t afforded
| simple and natural explanations for phenomena
which had previously been clouded by rather
| strained assumptions.
Twentythree years later, in 1888, Sir VIM.
thomson brought q powerful reinforcement to
the elastic theory. He showed, as did Green,
that the compression wave, which theory called
for and which did not exist in fact might be
got rid of in the theory by making the velocity
OF the compression wave zero instead of in
finite. Thomson found what had escaped Green,
that this assumption did not involve I'M
stable condition of the medium, and that there
fore 1t was admissible 1t was also shown at
once by Thomson, Willard Gibbs and Fltz-
gerald that this new and rather startling sug
gestlon placed the elastic and electric theories
on the same logical basis if the ether was con-
sidered incompressible in the electric theory
and to have rigidity zero for a compression
wave In the elastic theory. 1t is, in fact, worthy
OF remark, as a matter of cOngratulation, show
ing how far scientific men have emerged from
the intellectual pugilism of last century, that
Thomson's audaciOus departure was met with
pleased surprise instead Of with angry polemlcs
against a new heresy.
The showing up of lightin space occupied by
matter shows that the ether within must either
be more sense (as Fresnel believed) or less
elastic than that existing in free space. 1t is
certainly very difficult to understand what
there can be in the molecules of matter which
can Increase the density of an incOmpressible
medium The beautiful experiment OF Michel
son and Morley shows apparently that the
ether at the surface of the earth moves with it.
1t is dragged along as if it were vivid liquid.
The field Of steel magnet is, however. a rota-
tional phenomenon. 1t is spin which is
maintained permanently without the expend-
lture OF energy. 1t seems therefore that the re-
slstance to shear which shows itself in the adhe-
sion of the ether to the moving earth must be
rlgltlty due In some way to motion. Other
experiments OF Nicholson and Morley on the
motion of light in moving columns of water
have been taken as proof that the ether in
water Is condensed to nine-sixteenths of it's
volume in air. The ether in water certainly
behaves as If 1T were more dense, but it is
another matter to say that it is So 1t seems
improbable. 1t is still mathematical fiction
which covers gap in our knowledge of the
ether The speaker thought that the expert
ment should be repeated with water at rest
within tube which should be mounted on
elastic supports in moving railway car. The
water tube and observers seat should be
rigidiy connected and swung on dampened
spring supports from the top and sides of the
car. The question to be settled is whether the
ether or any part of it is at rest in space and
does it sweep through the interior OF bodies
which move through it as wind sweeps through
the leaves and branches of a tree. This form
OF the experiment is the one contemplated by
Elsenlohrs analysis leading to Fresnel's
formula, and it is capable of great variations
In the conditions of experiment. 1t is, how
ever, more difficult and moro expensive than
the one SO we'll executed by Nicholson and
Morley. Whatever its results may be it
promises to add greatly to our knowledge of
the physics of the ether.