PRINCIPLES OF MATHEMATICAL PHYSICS 619 



of a second. Then it would be seen that the amplitude of the oscil- 

 lation depends not alone on the variation of the motion, variation 

 which is well known, since it is the motion of our globe on its elliptic 

 orbit, but on the mean value of this motion; so that the constant of 

 aberration would not be altogether the same for all the stars, and the 

 differences would tell us the absolute motion of the earth in space. 



This, then, would be, under another form, the ruin of the prin- 

 ciple of relativity. We are far, it is true, from appreciating the 

 thousandths of a second, but after all, say some, the total absolute 

 velocity of the earth may be much greater than its relative velocity 

 with respect to the sun. If, for example, it were 300 kilometers per 

 second in place of 30, this would suffice to make the phenomena 

 observable. 



I believe that in reasoning thus we admit a too simple theory 

 of aberration. Michelson has shown HS, I have told you, that the 

 physical procedures are powerless to put in evidence absolute mo- 

 tion; I am persuaded that the same will be true of the astronomic 

 procedures, however far one pushes precision. 



However that may be, the data astronomy will furnish us in 

 this regard will some day be precious to the physicist. While wait- 

 ing, I believe the theorists, recalling the experience of Michelson, 

 may anticipate a negative result, and that they would accomplish 

 a useful work in constructing a theory of aberration which would 

 explain this in advance. 



But let us come back to the earth. There also we may aid the 

 experimenters. We can, for example, prepare the ground by study- 

 ing profoundly the dynamics of electrons; not, be it understood, 

 in starting from a single hypothesis, but in multiplying hypotheses 

 as much as possible. It will be, then, for the physicists to utilize 

 our work in seeking the crucial experiment to decide between these 

 different hypotheses. 



This dynamics of electrons can be approached from many sides, 

 but among the ways leading thither is one which has been somewhat 

 neglected, and yet this is one of those which promise us most of sur- 

 prises. It is the movements of the electrons which produce the line 

 of the emission spectra; this is proved by the phenomenon of Zee- 

 mann; in an incandescent body, what vibrates is sensitive to the 

 magnet, therefore electrified. This is a very important first point, 

 but no one has gone farther; why are the lines of the spectrum 

 distributed in accordance with a regular law? 



These laws have been studied by the experimenters in their least 

 details; they are very precise and relatively simple. The first study 

 of these distributions recalled the harmonics encountered in acous- 

 tics; but the difference is great. Not only the numbers of vibrations 

 are not the successive multiples of one number, but we do not 



