240 SCIENCE AND' METHOD. 



effects of the wave of acceleration are constantly 

 accumulating, but this accumulation itself is so slow 

 that it would certainly require thousands of years of 

 observation before it became perceptible. 



Let us therefore make the calculation, taking the 

 motion as quasi-stationary, and that under the three 

 following hypotheses : — 



A. Admitting Abraham's hypothesis (undeformable 

 electrons), and retaining Newton's law in its ordinary 

 form. 



B. Admitting Lorentz's hypothesis concerning the 

 deformation of the electrons, and retaining Newton's 

 ordinary law. 



C. Admitting Lorentz's hypothesis concerning the 

 electrons, and modifying Newton's law, as in the fore- 

 going section, so as to make it compatible with the 

 Principle of Relativity. 



It is in the motion of Mercury that the effect will 

 be most perceptible, because it is the planet that has 

 the highest velocity. Tisserand formerly made a 

 similar calculation, admitting Weber's law. I would 

 remind the reader that Weber attempted to explain 

 both the electrostatic and the electro-dynamic phe- 

 nomena, assuming that the electrons (whose name had 

 not yet been invented) exercise upon each other attrac- 

 tions and repulsions in the direction of the straight 

 ..... ^ 



Ime jommg them, and depending not only upon their 



distances, but also upon the first and second deriva- 

 tives of these distances, that is consequently upon 

 their velocities and their accelerations. This law of 

 Weber's, different as it is from those that tend to gain 

 acceptance to-day, presents none the less a certain 

 analogy with them. 



