THEORY OF RELATIVITY 
273 
It was also H. A. Lorentz who adopted the so-called contraction 
theory, first suggested by Fitzgerald, to satisfy his equations in 
connection with electron motion ; assuming the contraction to be 
real the electrons taking on ellipsoidal form with their shorter 
axes in the direction of motion; hence the term '‘Lorentz contrac- 
tion/’ In this theory there would, however, be involved some 
relation of this contraction to a corresponding physical change 
within the electron varying with the speed of the electron of 
which there is no trace. Einstein solved the enigma with one 
stroke by establishing the relativity of time and space leading 
to the same Lorentz equations but on a more rational basis. 
Prof. Lorentz has the following to say in his Columbia lectures 
already referred to: “ . . . he (Einstein) may certainly take 
credit for making us see in the negative result of experiments 
like those of Michelson, Rayleigh and Brace, not a fortuitous 
compensation of opposite effects, but the manifestation of a gen- 
eral and fundamental principle.” And again : “It would be un- 
just to add that, besides the fascinating boldness of his starting 
point, Ein-itein’s theory has another marked advantage over 
mine, whereas I have not been able to obtain for the equations 
referred to moving axes ‘exactly’ the same form as for those 
which apply to a stationary system, ‘Einstein’ has accomplished 
this by means of a system of new variables slightly different 
from those which I have introduced.” 
This was written in 1909 four years after the publication of 
Einstein’s work on the Restricted theory, after the theory had 
been tested by Kaufman and Bucherer in connection with the ex- 
tremely rapid moving /3-rays establishing the forms for the longi- 
tudinal and transverse mass of the electron as : 
mo mo 
m,= ^ ni(. = 
V(I=|)» v“i=| 
distinguishing between the instantaneous motion in the x-di- 
rection as transverse, attaching these terms to the respective 
masses. At the present time the form has been simplified agree- 
ing with that given by Lorentz in 1904, namely : 
mo 
m= 
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