THE PATH OP EVOLVTIOtf 



at 40,000 kilometers a second, though probably much 

 greater.* Thus constituted the Ether forms the me- 

 dium whose vibrations produce the phenomena of radi- 

 ant heat, light and electricity in a manner somewhat 

 analogous to the transfer of sound by waves of the 

 air. The air is known to be composed of gaseous 

 molecules moving in all directions with great rapidity, 

 but yet it acts as a molar medium to receive and 

 transmit together without confusion the often varied 

 and extremely complicated vibrations that constitute 

 Sound. Thus the Ether somewhat resembles a gas, 

 but differs therefrom by being throughout of uniform 

 density and in being non-compressible, since it pene- 

 trates through all bodies and cannot be confined ; nor 

 can it be compressed as air is by its own mass, for it 

 is not ponderable matter, not being affected by 

 gravity. The vibrations of radiant heat, light, etc., 

 which it transmits are transverse vibrations per- 

 pendicular to the line of transition (not like the 

 aerial vibrations that constitute sound, the waves of 

 which are in the line of transition and are like the alter- 

 nate swellings and contractions of concentric spheres). 

 It is this fact, that the ether ic waves are transverse 

 vibrations, that has seemed to require that the Ether 

 should possess the incomprehensible kind of solidity 

 often ascribed to it, so that it might have the desired 



* The latest experiments (1902) give about half that of light. 

 '34 



