108 MODERN THEORIES OP ELECTRICITY AND MATTER. 



recalls the old idea of two electrical fluids, only that we distinguish 

 clearly the atomic structure of these fluids, and we understand bet- 

 ter the relations which exist between the atoms of electricity and 

 matter, a relation which is the most important aspect of the problem. 



An atom of electricity in motion produces around itself an electro- 

 magnetic field which accompanies the movement of the particle, and 

 which represents a certain quantity of energy whose amount is 

 greater the higher the velocity of the charged projectile. It is not 

 ])ossible to increase this velocity without the expenditure of energy, 

 and in consequence the charged projectile is endowed with a certain 

 inertia. In mechanics inertia is used as a measure of the mass, and we 

 may say that the atom of electricity possesses mass on account of its 

 charge. Computation shows that the mass depends upon the velocity. 

 It remains constant when the velocity of the projectile is small (about 

 one one-hundredth the velocity of light), but for increasing velocities 

 it augments very rapidly and tends toward an infinite value when the 

 velocity approaches that of light, so that this is a limiting velocity 

 which can not be realized. 



It may be imagined that a group of atoms of electricity, both posi- 

 tive and negative, whose total charge is zero, possesses, nevertheless, 

 inertia in consequence of the constituent electrical charges. This 

 group might serve as a model of a material atom. Thus may be 

 ]>roposed a more general form of mechanics than that customarily 

 considered, which is based on the constancy of mass. The latter 

 would be no more than a first approximation to the truth, and holds 

 good only for cases of motion where the velocity is not extremely 

 great. Preliminary attemj^ts have been made to explain universal 

 gravitation between atoms constituted as above proposed. Alto- 

 gether these studies tend toward an intimate fusion of the idea of 

 electricity and the idea of matter, so that these two conceptions may 

 yet be actually identified. 



This proposed constitution of the atoms serA^es as an excellent 

 foundation for a theory of the emission of light or radiation by a 

 body. Such emission may be regarded as consisting of electro-mag- 

 netic waves of short period, emitted by an atom whose constituent 

 ions are in a state of vibration. The same atomic structure serves 

 also very well in the case of radioactive atoms. These atoms are in 

 fact emitting corpuscles, some of which are electrons, others positivel}^ 

 charged particles having a size comparable with that of atoms. 



But we will not now penetrate further the domain of these theories, 

 but turn rather to examine some of the phenomena which have served 

 as a foundation for their development. It is well known that gases 

 in their ordinary state, when exposed to a weak electrical field, have 

 so insignificant a conductibility that they are regarded as remarkably 

 good insulators. But it is not the same when the gases are under 



