THE VELOCITY OF LIGHT 55 



the light-flash is not in the least analogous to the 

 evasiveness of the rainbow. 



But although this explanation may help to reconcile 

 us to what at first seems a blank impossibility, it is not 

 really the most penetrating. You will remember that 

 a Seen-Now line, or track of a flash of light, represents 

 the grain of the world-structure. Thus the peculiarity 

 of a velocity of 299,796 kilometres a second is that it 

 coincides with the grain of the world. The four- 

 dimensional worms representing material bodies must 

 necessarily run across the grain into the future cone, and 

 we have to introduce some kind of reference frame to 

 describe their course. But the flash of light is exactly 

 along the grain, and there is no need of any artificial 

 system of partitions to describe this fact. 



The number 299,796 (kilometres per second) is, 

 so to speak, a code-number for the grain of the wood. 

 Other code-numbers correspond to the various worm- 

 holes which may casually cross the grain. We have 

 different codes corresponding to different frames of 

 space and time; the code-number of the grain of the 

 wood is the only one which is the same in all codes. 

 This is no accident; but I do not know that any deep 

 inference is to be drawn from it, other than that our 

 measure-codes have been planned rationally so as to turn 

 on the essential and not on the casual features of world- 

 structure. 



The speed of 299,796 kilometres per second which 

 occupies a unique position in every measure-system is 

 commonly referred to as the speed of light. But it is 

 much more than that; it is the speed at which the mass 

 of matter becomes infinite, lengths contract to zero, 

 clocks stand still. Therefore it crops up in all kinds of 

 problems whether light is concerned or not. 



