CONSEQUENCES OF THE CONTRACTION n 



is now exaggerating vertical distances to twice the scale 

 of horizontal distances. 



"Very well", you reply, "I will not get up. I will lie 

 in bed and watch you go through your performance in 

 an inclined mirror. Then my retina will be all right, 

 but I know I shall still see no contraction." 



But a moving mirror does not give an undistorted 

 image of what is happening. The angle of reflection of 

 light is altered by motion of a mirror, just as the angle 

 of reflection of a billiard-ball would be altered if the 

 cushion were moving. If you will work out by the 

 ordinary laws of optics the effect of moving a mirror at 

 161,000 miles a second, you will find that it introduces 

 a distortion which just conceals the contraction of my 

 arm. 



And so on for every proposed test. You cannot 

 disprove my assertion, and, of course, I cannot prove 

 it; I might equally well have chosen and defended any 

 other velocity. At first this seems to contradict what 

 I told you earlier — that the contraction. had been proved 

 and measured by the Michelson-Morley and other experi- 

 ments — but there is really no contradiction. They were 

 all null experiments, just as your experiment of watch- 

 ing my arm in an inclined mirror was a null experiment. 

 Certain optical or electrical consequences of the earth's 

 motion were looked for of the same type as the 

 distortion of images by a moving mirror; these would 

 have been observed unless a contraction occurred of 

 just the right amount to compensate them. They 

 were not observed; therefore the compensating contrac- 

 tion had occurred. There was just one alternative; the 

 earth's true velocity through space might happen to 

 have been nil. This was ruled out by repeating the 

 experiment six months later, since the earth's motion 



