234 BODIES SMALLER THAN ATOMS. 



culculated, and dividino- the whole volume of water b}^ 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 6.6 X 10"^" electrostatic units of electricity or 2. IT X 10"^ • 

 electro-magnetic units. According to the kinetic theory of gases 

 there are 2 X K)''' molecules in a cubic (jentimeter of gas at iitmos- 

 pheric pressure and at the temperature 0'^ C. ; as a cubic centimeter of 

 hj^drogen weighs about I'll of a milligram each molecule of hydrogen 

 weighs about 1 (22 X 10") milligrams, and each atom therefore about 

 1/(11:X 10") milligrams, and as we have seen that in the electrolysis of 

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

 hydrogen will carry a charge equal to 10/ (11 X 10") = 2.27 X 10-=^" 

 electro-magnetic miits. The charge on the particles in a gas we have 

 seen is equal to 2.17 X 10^'^** units; these numbers are so nearh^ 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 electrol3^sis. This result has been verified in 

 a different Ava}' 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 onl}'^ 

 about one one-thousandth of that of a hydrogen atom. These particles 

 occurred in the cathode rays inside a discharge tulje, 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 recognized. These negatively electrified particles, which I 

 have called corpuscles, 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 mole- 

 cules 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. 



In fact, in every case in which the transport of negative electricity 

 through gas at a low pressure (i. e. , when the corpuscles have nothing 



