Space Forum / Astronomy / October 2006

Out of historical interest, I have long sought to find again a
reference to the first person to propose a theory such as what Curt
Renshaw now calls his Radiation Continuum Model (RCM), the idea that
light may travel at many different speeds, but that we can only
percieve it at one speed.  I found it!  It was the great French
scientist of the early nineteenth century, Dominique François Jean
Arago.

"II. ARAGO’S EXPERIMENT  As was already mentioned, Arago thought that
the refraction of a light ray by a prism depended on the velocity of
the prism. Specifically, Arago stated that only the velocity of light
relative to the prism should enter the refraction law. Thus, since the
prism moves together with the Earth, a starlight ray would suffer
different deviations depending on thedirection of the ray with respect
to the motion of the Earth. These differences would turn out to be
maximal between rays traveling in the same direction as the Earth and
rays traveling in the opposite direction.

Arago mounted an achromatic prism on the objective lens of a telescope,
and he observed several stars through the prism. By comparing this
apparent position with the real position of each star, Arago determined
how the prism deviated the light rays coming from each star.He expected
different angles of deviation for different stars. However, Arago
declared: “the rays of all stars are subjected to the same
deviations; the slight differences found do notfollow any law”.

Arago made the measurements in two different times of the year. On
March 19 and March27, he utilized a prism of 24◦and a mural telescope
to measure the distances from the starsup to the zenith. On October 8,
Arago used a larger prism to cover a half of the objective lens of an
improved telescope (namely a repeating circle), which permitted more
precise measurements. In this way, the telescope could receive the
starlight directly from the star or previously deviated by the prism
(the angle between these two different directions, corrected by the
time elapsed between both measurements, was the deviation angle). The
results are reproduced in Tables I, II and III (the measurements are
displayed in the way Arago did it; besides we added the approximated
times when the stars passed by the Paris meridian to help in locating
the stars in the sky, as Fig. 1 shows). The motion of the earth around
the Sun (30 km/s) was enough to generate meaningful differences in the
deviation angle ofstars passing the meridian at 6.00 a.m. and stars
passing it at 6.00 p.m. In the first case,the starlight is opposite to
the motion of the Earth; in the second one, the starlight goes inthe
same direction than the Earth. For these two extreme cases, Arago
expected differences of 12” with the prism of 24◦ used in March,
and 28” in the measurements performed inOctober. However, there were
no traces of any composition of motion entering Snell’s lawin the
results obtained by Arago.

Arago convinced himself that the only possible interpretation of his
null result, in the context of the corpuscular model, was that the
sources emit light with all sort of velocities.But our eyes are only
sensitive to a narrow band of them. Thus, we are always detecting the
same kind of corpuscles, and no differences can be found in their
refraction. Concerning the wave theory of light, Arago said that “the
explanation for the refraction in this theory is based on a simple
hypothesis that is very difficult to submit to calculation. Therefore,
I cannot determine in a precise way whether the velocity of the
refractive body has some influence on the refraction...”"

http://209.85.135.104/search?q=cache:xb0HzyEKrSQJ:arxiv.org/pdf/physics/0412055+
%22Fresnel%22+%22water+filled+telescopes%22&hl=en&gl=us&ct=clnk&cd=4

http://chem.ch.huji.ac.il/~eugeniik/history/arago.html

Double-A