346 GENERAL SCIENCE 



quency for the eye to recognize. Photographic plates put 

 out in this ultra-violet region, and kept wholly screened from 

 any light (ether waves capable of affecting the eye), suffer 

 much the same changes as when exposed to sunlight. In 

 fact the best part of sunlight for photographic purposes is that 

 of the violet end of the spectrum. It is said to be rich in 

 actinic rays. 



At the other end of the spectrum, and beyond the red of the 

 spectrum sufficiently far to be in a region destitute of light, 

 delicate thermal (heat) instruments detect the existence of 

 long ether waves (waves of lesser frequency). These waves 

 are incapable of affecting the eye to produce light sensations, 

 but they are capable of heating effects. Not only are there 

 ether waves recognized by us as heat and light, but there are 

 electric waves propagated through space which are inti- 

 mately related to the other wave motions. Perhaps the best 

 illustration of this to-day is the transmission of electric sig- 

 nals through the ether medium in wireless telegraphy. 

 There is suggested in all this the possibility that all the so- 

 called " forces," or forms of energy, transmitted through 

 space without dependence upon any material medium, are 

 closely related to one another and to the ether as a medium 

 of transmission. It suggests, too, the possibility of forces 

 wholly unknown to man as yet, and perhaps never to become 

 known by reason of lack of any means by which to compre- 

 hend them. 



SUMMARY 



Light is one of the forms of energy, and is capable of affecting the 

 eye to cause sight or vision. Without eyesight knowledge of the exist- 

 ence of light would be impossible. At the same time light exists 

 whether or not there be any eye to receive and take note of it. The 

 study of light in Physics has little to do with sight as a sensation. 



The accepted theory concerning the nature of light supposes the 

 existence of a medium known as ether, and the transmission of the 



