1901.] on the Existence of Bodies Smaller than Atoms. 577 



deposited by cooling the air can easily be calculated, and, dividing 

 the whole volume of water by the volume of one of the drops, we get 

 the number of drops, and hence the number of the electrified particles. 

 We saw, however, that if we knew the number of particles we could 

 get the electric charge on each particle : proceeding in this way I 

 found that the charge carried by each particle was about 6 ■ 5 X 10 -10 

 electrostatic units of electricity, or 2*17 X 10~ 20 electro-magnetic 

 units. According to the kinetic theory of gases, there are 2 X 10 19 

 molecules in a cubic centimetre of gas at atmospheric pressure 

 and at the temperature 0° C. ; as a cubic centimetre of hydrogen 

 weighs about one-eleventh of a milligram, each molecule of hydrogen 



weighs about — — — — r milligrams, and each atom therefore about 



milligrams, and as we have seen that in the electrolysis 



(U X 10 19 ) . 



of solutions one-tenth of a milligram carries unit charge, the atom of 



hydrogen will carry a charge equal to ^ 10") = 2-27 X lO" 20 



electro-magnetic units. The charge on the particles in a gas, we 

 have seen, is equal to 2 ■ 17 X 10~ 20 units. These numbers are so nearly 

 equal that, considering the difficulties of the experiments, we may 

 feel sure that the charge on one of these gaseous particles is the same 

 as that on an atom of hydrogen in electrolysis. This result has been 

 verified in a different way by Professor Townsend, who used a method 

 by which he found, not the absolute value of the electric charge on a 

 particle, but the ratio of this charge to the charge on an atom of 

 hydrogen ; and he found that the two charges were equal. 



As the charges on the particle and the hydrogen atom are the same, 

 the fact that the mass of these particles required to carry a given 

 charge of electricity is only one-thousandth part of the mass of the 

 hydrogen atoms shows that the mass of each of these particles is only 

 about Tt ,V(T °f * na * °f a hydrogen atom. These particles occurred in 

 the cathode rays inside a discharge tube, so that we have obtained from 

 the matter inside such a tube particles having a much smaller mass 

 than that of the atom of hydrogen, the smallest mass hitherto recog- 

 nised. These negatively electrified particles, which I have called cor- 

 puscles, have the same electric charge and the same mass whatever be 

 the nature of the gas inside the tube or whatever the nature of the 

 electrodes ; the charge and mass are invariable. They therefore form 

 an invariable constituent of the atoms or molecules of all gases, and 

 presumably of all liquids and solids. 



Nor are the corpuscles confined to the somewhat inaccessible 

 regions in which cathodic rays are found. I have found that they are 

 given off by incandescent metals, by metals when illuminated by 

 ultra-violet light, while the researches of Becquerel and Professor and 

 Madame Curie have shown that they are given off by that wonderful 

 substance the radio-active radium. 



Vol. XVI. (No. 95.) 2 q 



