200 THE REALITIES OF MODERN SCIENCE 



electrons do not come to rest immediately, but only 

 after they have expended the kinetic energy which was 

 originally imparted to them. 



In terms of energy we think of a system of electrons 

 as having potential energy which is reduced if they 

 are set in motion along parallel lines. The reduction 

 will depend upon the velocity of the electrons. When 

 will the p.e. be zero, and can two electrons ever attract ? 

 The answer to both questions comes in the statement 

 that two electrons moving with the velocity of light 

 do not pellate. The velocity of light is that with which 

 all radiations from electrons are transmitted through 

 a vacuum. It has the enormously high value of 3 X 10 10 

 cm. per sec., and appears to be the upper limit for 

 velocity in our universe. Whatever the ether may 

 be it cannot transmit disturbances faster than this. 1 

 Of course, where electromagnetic disturbances are im- 

 peded in their passage through the ether by the pres- 

 ence of groups of electrons, as for example when light 

 passes through a piece of glass, the velocity may be 

 smaller than the value given above. The velocity of 

 light represents tne greatest velocity we can imagine 

 in a universe built up, as is ours, of electrons. Two 

 electrons, then, can never tractate but may be moving 

 so fast that they do not pellate. Thus if an atom could 

 be shot off through space with the velocity of light 

 there would be no tractation of its nucleus and elec- 

 trons. There would, then, be nothing to prevent the 



1 Media which transmit energy do so as a result of their elasticity, 

 the velocity of propagation in each being determined by its con- 

 stants of elasticity. For each substance there is therefore a definite 

 velocity. The ether behaves like an elastic medium and transmits 

 all disturbances at a definite rate. 



