226 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



These conclusions have been clenched by yet later experiments. 

 Hupka ^ used the electrons from the photo-electric effect, produced in 

 a very perfect vacuum and accelerated by intense electric fields 

 reaching a strength of 90,000 volts. The knowledge of the velocity 

 V and the ratio e/m was deduced from the magnetic deviation, 

 rendered evident by a fluorescent screen, and the magnitude of the 

 accelerating potential. The maximum velocities obtained were of 

 the order of v/^. The formula of Lorentz fits tliese observations also 

 better than that of Abraham. However, these experiments are less 

 convincing than the preceding ones, as Heil noted,^ since the highest 

 potentials must be known with a precision greater than 1 per cent, an 

 accuracy difficult to obtain. 



C. E. Guye and Eatnovsky,^ desirous of escaping this difficulty, 

 used ordinary cathode rays, produced in a good vacuum, and deviated 

 at the same time botli electrically and magnetically so as to get rid 

 of the necessity of measuring the potential used. These results also 

 confirm Lorentz's formula at the expense of Abraham's. 



We are led by all these results to look upon an electron as deform- 

 able only in the direction of its motion, conformable with the prin- 

 ciple of relativity; in this respect they undergo the contraction of 

 Lorentz (see further on). Do all difficulties now disappear? With- 

 out considering the objections of a more general nature which are 

 to-day urged against the principle of relatively (see Sec. II), we 

 must say, no. As H. Poincare * has observed, we can not comprehend 

 why an electron does not disintegrate spontaneously under the in- 

 fluence of the electric and magnetic forces due to its charge unless 

 there comes into play, in order to maintain equilibrimn, other forces 

 from without analogous to pressure. We are led thus to introduce 

 something further than pure electromagnetism as a basis of our new 

 mechanics. We are just as far as ever from comprehending the 

 primordial forces underlying matter. 



II. THE PRINCIPLE OF RELATIVITY. 



Lorentz has shown that the electromagnetic theory furnishes an 

 explanation of the negative results of the experiments which were 

 expected to demonstrate, either by electrical or optical means, the 

 movement of translation of the earth relative to the supposed sta- 

 tionary ether. These experiments could detect only the effects of 

 the first order w^ith reference to ^ (quotient of the velocity of trans- 

 lation of the earth, r, relative to tlie velocity of light, V), while 



1 Hupka, Verb, der Deutsch. Phys. Gesellsch., vol. 11, p. 249, 1909; Annalen der Physik, 

 1910. 

 = Heil, Annalen der Physik, vol. 31, p. 519, 1910. 

 3 Guye and Ratnovsky, Comptes Rendus, CL, p. 326, 1910. 

 * II. Poincar^, Rendiconti del Circolo Math, di Palermo, vol. 21, p. 129, 1906. 



