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interest, as it has since—and it is well known—achieved considerable practical and
scientific significance, for instance, as a source for ultraviolet light. Some original
work on galvanic polarization must also be mentioned. Together with Heinrich
Rubens he proved for several dielectric fluids that the dielectric constant as ob-
tained from experiments with Hertzian waves is equal to the one measured under
static conditions.
Arons proved in 1885 the validity of the Helmholtz relation between the vapor
pressure of solutions and their heat of dilution; he did this by making clever math-
ematical use of already-known experimental data. From a variety of individual pa-
pers—occasionally based upon a lucky idea—we want to mention an especially
nice demonstration of Hertzian electrical waves in conductors. Arons stretched
wires for standing waves lengthwise inside a Geißler tube, so that the tube glowed
at locations of maximum electric voltage, indicating by its glow the distribution of
the alternating electrical field.
The researcher, for years barred from the laboratory due to a severe ailment, did
his last great work in 1912. Arons attacked the problem of expressing the colors of
a body by numbers such that they could be reconstructed from these numbers at any
time, using a suitable apparatus. This is the same task on which Ostwald worked
with great care in recent years. The practical importance of this subject matter is
obvious. If this method would have been perfected centuries ago, we would today
know what the colors on the pictures of the great painters of past generations
looked like. In order to solve the problem, Arons used a method of optical inter-
ference whereby he removed a numerically uniquely determined section of day-
light, reflected from a matte white surface. The removal was accomplished by
quartz plates of known thickness and polarizers in known angular positions.
These lines can only project a vague image of the tireless work of the man. He
produced modest solid work as a scientist, while as a human being he was striving
for what—in his opinion—justice in our time demanded. Honor to his memory!
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