9 8 D O C . 2 4 L E O A R O N S A S P H Y S I C I S T
24. “Leo Arons as Physicist”
[Einstein 1919e]
Published 17 November 1919
In: Sozialistische Monatshefte 53 (1919): 1055–1056.
The physicist Leo Arons has left us after suffering a long time. With him we lost
a man whose simple greatness will always be remembered by those who knew his
work and his life. His social compassion and his struggle for justice have led him
to the circle of socialists, motivated him to present his socialist convictions in pub-
lic, notwithstanding the severe difficulties and animosities he had to suffer in a re-
actionary-led state. He was one of those personalities, so rare among our
academicians, who represented not only spiritual autonomy but also independence
of character, unaffected by the prejudices of his class and with the exemplary cour-
age to make sacrifices. He acted on what he saw as self-evident, with simplicity and
without the grand gesture of a martyr.
As a physicist I, who neither knew the deceased nor belonged to his circle of ac-
tivists, shall recall his scientific work only as it is revealed in his publications. The
non-expert who sees a small bundle of papers that represents the lifelong work of
a physicist has no idea how difficult it is to wrest these seemingly inconspicuous
results from the prudish matter (Materie). The individual researcher, however, has
the satisfaction that his hand-made building blocks have become permanent parts
of the solid structure of his science.
Aron’s lifework was primarily dedicated to the empirical research of electrical
phenomena that are governed by Maxwell’s theory. Already his 1884 dissertation,
devoted to a rigorous measurement of the rotation of the plane of polarized light by
a magnetic field, is part of this complex of problems. In 1888, he verified in a care-
ful investigation Maxwell’s theory of residual charges in dielectric substances by
showing that the occurrence of residual charges in capacitors derives from the in-
homogeneity of the dielectric that affects conductivity. Of lasting significance are
also his investigations of the dielectric constants of conducting fluids, which he
carried out, in part, with Emil Cohn. Together with him he found, in 1888, the ab-
normally large dielectric constant of water. In 1892 Arons was the first to discover
the mercury arc (mercury vapor lamp), something that also may be of general
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