CONSTITUTION OF MATTEE BECQUEREL. 283 



when the velocity approaches the velocity of light (300,000 kilo- 

 meters per second). 



We have seen that it is possible to measure the velocity as well as 

 the ratio of charge to mass in the (3 particles of radium. These 

 (3 rays form a sheaf of corpuscles which have very different velocities 

 and certain of them attain velocities closely approaching that of 

 light. We understand also that the greater the velocity the smaller 

 the ratio of the charge to the mass; that is to saj'', inasmuch as the 

 charge can not vary, the greater the mass becomes. This, to be sure, 

 is just what we should expect, and the law of variation of the total 

 mass in terms of the velocity should indicate the relative parts of 

 the two masses in the total mass. 



The result is surprising; the variation of the total mass is the 

 same as if the electromagnetic mass existed alone, consequently the 

 TThaterial TYiass appears to he zero. In other words, the electron is 

 made up of electricity free from any material support, and is a modi- 

 fication, still unidentified in other ways — perhaps of a whirling na- 

 ture — of the medium which we call the ether. 



Thus we find that the electron is a particular condition of the ether ; 

 it has a little the nature of matter in that it possesses mass, which is 

 one of the fundamental properties of matter, nevertheless it is not 

 material in the sense which has heretofore been attributed to the 

 word, since its inertia is merely the inertia of the ether. To sum up, 

 we may picture the electron as an intermediate state between the 

 ether and ponderable matter. 



The mass of the negative electron at low speeds is 0.5X10""' gram.^ 

 Assuming it to be spherical its radius can be calculated, its mass 

 and charge being known. This is found to be 10"^^ centimeter. 



Up to the last few years physicists were always driven to seek a 

 mechanical explanation of physical phenomena. It is due to this, for 

 instance, that Fresnel originated a mechanical theory of light. Such 

 an attempt was very natural, since mechanical phenomena fall under 

 our observation every day and are much more familiar to us than 

 electrical phenomena. 



Nevertheless, although according to the theory of Maxwell a 

 mechanical explanation, or speaking more exactly an infinite num- 

 ber of mechanical explanations of electromagnetic phenomena, are 

 possible, still no satisfactory interpretation has been obtained in this 

 manner, and the ether has appeared to be very different from the 

 bodies of which we have knowledge. 



In view of the data which have now been acquired, however, men 

 of science have decided not only to search no longer for a mechan- 

 ical explanation of electromagnetism, but to formulate an electrical 



