INFINITY OF THE UNIVERSE IOI 



suggests a fairly conclusive argument against either 

 possibility. Whenever energy is radiated by wave- 

 motion, and the waves arrive at the limit of the 

 medium capable of transmitting the motion, they 

 are totally reflected. And whether we have an 

 etherless envelope round our system or a perfect 

 reflector, we must expect to receive from it a uni- 

 form famt luminosity and a uniform slight heat. 

 Whatever may be said about the real source of the 

 so-called stellar heat, there is no doubt that the 

 faint luminosity is entirely wanting in many parts 

 of the heavens. Vega gives us about the same 

 quantity of heat as a candle ten miles away, and 

 Arcturus double that quantity. In the starless 

 portions of the sky no radiant heat is discoverable. 

 If it exists, it is below the limits of our measuring 

 instruments. This suggests, therefore, that if there 

 is a supra-world, it is a cold and dark world, or, 

 at least, that it would appear cold and dark to us. 

 Not so, as we shall see, to its own inhabitants. 



Our measuring instruments of light and heat fail, 

 so far, to establish the existence of anything outside 

 our stellar system. On the other hand, they do 

 not disprove the existence of a whole surrounding 

 universe <>t' ML liar systems which arc comparatively 

 dark and cold. But our theoretical resources are 

 not yet exhausted. Wherever we have a force or 

 form of energy whose action across interstellar space 

 is known, we may employ that agency for testing 



