THE VALUE OF SCIENCE 349 



to change the definition of mass; we can not any longer distinguish 

 mechanical mass and electrodynamic mass, since then the first would 

 vanish; there is no mass other than electrodynamic inertia. But in 

 this case the mass can no longer be constant; it augments with the 

 velocity, and it even depends on the direction, and a body animated 

 by a notable velocity will not oppose the same inertia to the forces 

 which tend to deflect it from its route, as to those which tend to accel- 

 erate or to retard its progress. 



There is still a resource; the ultimate elements of bodies are elec- 

 trons, some charged negatively, the others charged positively. The 

 negative electrons have no mass, this is understood; but the positive 

 electrons, from the little we know of them, seem much greater. Per- 

 haps they have, besides their electrodynamic mass, a true mechanical 

 mass. The real mass of a body would, then, be the sum of the mechan- 

 ical masses of its positive electrons, the negative electrons not count- 

 ing; mass so defined might still be constant. 



Alas ! this resource also evades us. Recall what we have said of 

 the principle of relativity and of the efforts made to save it. And it 

 is not merely a principle which it is a question of saving, it is the in- 

 dubitable results of the experiments of Michelson. 



Well, as was above seen, Lorentz, to account for these results, was 

 obliged to suppose that all forces, whatever their origin, were reduced 

 in the same proportion in a medium animated by a uniform transla- 

 tion ; this is not sufficient ; it is not enough that this take place for the 

 real forces, it must also be the same for the forces of inertia; it is 

 therefore necessary, he says, that the masses of all the particles be influ- 

 enced by a translation to the same degree as the electromagnetic masses 

 of the electrons. 



So the mechanical masses must vary in accordance with the same 

 laws as the electrodynamic masses ; they can not, therefore, be constant. 



Need I point out that the fall of Lavoisier's principle involves that 

 of Newton's? This latter signifies that the center of gravity of an 

 isolated system moves in a straight line; but if there is no longer a 

 constant mass, there is no longer a center of gravity, we no longer 

 know even what this is. This is why I said above that the experiments 

 on the cathode rays appeared to justify the doubts of Lorentz concern- 

 ing Newton's principle. 



From all these results, if they were confirmed, would arise an en- 

 tirely new mechanics, which would be, above all, characterized by this 

 fact, that no velocity could surpass that of light, 1 any more than any 

 temperature can fall below absolute zero. 



1 Because bodies would oppose an increasing inertia to the causes which 

 would tend to accelerate their motion; and this inertia would become infinite 

 when one approached the velocity of light. 



