Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Variation of Mass with Velocity: "Kugeltheorie" or "Relativtheorie"   This paper deals with four topics: The first subject is Abraham's spherical
electron, Lorentz's contracted electron and B\"ucherer's electron. The second
topic is Einstein's 1905 relativity theory of the motion of an electron.
Einstein obtained expressions for the longitudinal and transverse masses of the
electron using the principle of relativity and that of the constancy of the
velocity of light. The third topic is Einstein's reply to Ehrenfest's query.
Einstein's above solution appeared to Ehrenfest very similar to Lorentz's one:
a deformed electron. Einstein commented on Ehrenfest's paper and characterized
his work as a theory of principle and reasoned that beyond kinematics, the 1905
heuristic relativity principle could offer new connections between
non-kinematical concepts. The final topic is Kaufmann's experiments. Kaufmann
concluded that his measuring procedures were not compatible with the hypothesis
posited by Lorentz and Einstein. However, unlike Ehrenfest, he gave the first
clear account of the basic theoretical difference between Lorentz's and
Einstein's views. Finally, B\"ucherer conducted experiments that confirmed
Lorentz's and Einstein's models; Max Born analyzed the problem of a rigid body
and showed the existence of a limited class of rigid motions, and concluded,
"The main result was a confirmation of Lorentz's formula".

6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
19
The categories of this paper are: eess