182 THE NEW KNOWLEDGE. 



motion, which we understand to be inertia, and will thus 

 behave as though its mass were increased. In order that 

 this inertia, or increase of mass, should become perceptible, 

 it is necessary that the sphere should be very small and 

 that its speed should approach that of light. We can best 

 illustrate this by appending certain calculations subse- 

 quently made by Sir Oliver Lodge, showing the extent to 

 which the apparent mass would increase as the speed of 

 light is approached. If 1 equals the mass measured by 

 the inertia of the sphere under slow motions, at half the 

 speed of light the mass becomes 1.12; at three-quarters, 

 1.37; at nine-tenths, 1.8; when the speed is 99 per cent, 

 of that of light the mass is 3.28; at 99.5 per cent., 5; 

 while between this last value ana that of light the mass 

 increases to infinity. It is plain, then, that no substance 

 can move faster than light; and it is interesting to note 

 how very near the speed of light must be approached be- 

 fore the mass becomes increased to an enormous extent. 

 Now, this paper of Thomson's, at the time of its publica- 

 tion, excited but little comment because of the fact that 

 at that time no bodies were known which were sufficiently 

 small and sufficiently 'swift in their velocity to make this 

 increase in mass experimentally demonstrable. The paper 

 belonged to mathematical academics. It was not practi- 

 cally important. With the coming, however, of corpuscles, 

 the paper assumed a very different aspect. We have in 

 corpuscles particles very much smaller and very much 

 lighter than the smallest and lightest atom; and, more- 

 over, we have shown that in the case of radium these 

 particles are shot off with velocities approaching that of 

 light. We have, then, in the corpuscle a means of verify- 

 ing this mathematics and of determining, as a matter of 

 material fact, whether or not the mass measured by the 



