30 Life and Matter [chap. n. 



constant property we once thought it. It 

 is a function of velocity for one thing, and 

 when speeds become excessive the inertia of 

 matter rises perceptibly in value. The fact 

 that it would rise in value by a calculable 

 amount, and that the rise would be per- 

 ceptible when the speed of motion 

 approached in value to within, say, a tenth 

 of the velocity of light, was predicted mathe- 

 matically ; l and now, strange to say, it has 

 recently become possible to observe and 

 actually measure the increase of inertia 

 experimentally, and thus to confirm the 

 electrical theory not only as qualitatively 

 or approximately true, but as completely 

 and quantitatively accurate. A remarkable 

 achievement all this ! of quite modern times, 

 which has not excited the attention it 

 deserves save among physicists. 



But even this is not all that can be said as 

 to the fluctuating character of that funda- 

 mental material quality " inertia." It 

 appears possible, if electrons approach too near 



1 By Mr Oliver Heaviside and Professor J. J. Thomson. 



