THE WORLD BEYOND OUR SENSES 



for in the sunlight are both light and heat rays ; but 

 they might also sit and read in a room with a warm 

 stove that to us would be pitch dark. Their win- 

 dows might be made of thin plates of hard rubber, 

 to us entirely opaque, and they might look at the 

 sun and the moon through telescopes with lenses 

 made of the same material. Theirs would be a 

 world beyond our senses. 



So, too, with the other end of the spectrum, the 

 beyond- the- violet end. When Daguerre and others 

 found that upon certain delicate salts, like nitrate of 

 silver, light has a chemical action, they opened the 

 way for an exploration of the ultra-violet. For it 

 did not take long to find out that here again it was 

 a question of invisible forces. A large part of the 

 waves which affect a photographic plate does not 

 affect the eye at all. So it is possible, by means of 

 a prism and a little screen, to stop-out all the visible 

 part of the spectrum, and still take photographs 

 just as usual. There are the so-called actinic or 

 chemical rays, and in a chemist's hands they are 

 capable of a variety of actions. Had they been 

 known two or three centuries ago, men would surely 

 have thought they had found the philosopher's 

 stone, for these rays will turn one kind of phospho- 

 rus into another and quite different kind; they 

 will produce violent explosions, and make sub- 

 stances conduct electricity which otherwise do not. 



45 



