THE ELECTRICAL NATURE OF MATTER. 183 



inertia of a body increases with its velocity. This investi- 

 gation has been carried out by Kaufmann with the most 

 interesting results. These results are shown in the follow- 

 ing table. The first column expresses the relative veloci- 

 ties of the particle, and the second column the value of the 

 fraction e/m, where e is the charge on the particle and m 

 is its mass. 



Value of v. Value of e/m. 

 2.83 .62 



2.72 .77 



2.59 .975 



2.48 1.17 



2.36 1.31 



We see by this table, reading from bottom to top, that 

 the value of e/m diminishes as the velocity increases. We 

 learned in Part III, page 65, that the value of e remains 

 constant. Hence this table indicates that the mass in- 

 creases with the velocity. Kaufmann's work, therefore, 

 demonstrates, experimentally, the truth of Thomson's 

 mathematics. Not only so but it affords Professor Thom- 

 son the opportunity of still further extending the scope of 

 his mathematical conclusions. In a word, Thomson cal- 

 culates the ratio of the masses of the rapidly moving 

 corpuscles given out by radium to the mass of the same 

 particles when at rest, on the assumption that the whole of 

 the mass is due to the electrical charge upon it; and he com- 

 pares these results with the values as determined by Kauf- 

 mann' s experiments. The comparison is shown in the 

 following table, where the first column contains the ve- 

 locities as determined by Kaufmann, the second column 

 the mathematical determination of the number of times 

 the mass of a particle moving with the given velocity ex- 



