CLASSICAL AND NEW MECHANICS 159 



to be a constant, there remains only the alternative of 

 considering the mass of a body as a variable. This 

 evidently strikes at the very root of Newtonian me- 

 chanics. The effect of motion on mass is found to be 

 inappreciable until the velocity approximates to that of 

 light, so the discussion would have remained a purely 

 academic one, if the creation of the electron had not 

 brought us suddenly face to face with bodies which 

 are supposed to have a velocity great enough to affect 

 experimentally their mass. A further consequence of 

 this theory is that mass becomes infinite when the 

 velocity of light is reached. While that velocity has 

 always been considered enormous and beyond our 

 power to attain, such a result was entirely unsuspected. 

 The laws of mechanics of bodies at rest could evidently 

 no longer be held to be the same as those for bodies in 

 motion. 



Lastly, various experiments have been made to find 

 an effect due to the mutual relations of the ether and 

 matter. None could be found. One in particular, de- 

 vised by Professors Michelson and Morley, has proved 

 to be the hardest problem in modern physics to explain. 

 Calculation showed that certain properties of light 

 which depend on its velocity should be affected appre- 

 ciably by the motion of the earth through space, but 

 the experiment proved beyond doubt that such was not 

 the case. The first attempt at a reconciliation was 

 made by assigning certain complicated motions to the 



