276 The Outline of Science 



of deep-violet light-waves, which are Trr.W mcn - But light- 

 waves, the waves that affect the eye, are not the only waves car- 

 ried by the ether. Waves too short to affect the eye can affect 

 the photographic plate, and we can discover in this way the exist- 

 ence of waves only half the length of the deep -violet waves. Still 

 shorter waves can be discovered, until we come to those exces- 

 sively minute rays, the X-rays. 



Below the Limits of Visibility 



But we can extend our investigations in the other direction; 

 we find that the ether carries many waves longer than light- 

 waves. Special photographic emulsions can reveal the existence 

 of waves five times longer than violet-light waves. Extending 

 below the limits of visibility are waves we detect as heat-waves. 

 Radiant heat, like the heat from a fire, is also a form of wave- 

 motion in the ether, but the waves our senses recognise as heat 

 are longer than light-waves. There are longer waves still, but 

 our senses do not recognise them. But we can detect them by 

 our instruments. These are the waves used in wireless tele- 

 graphy, and their length may be, in some cases, measured in 

 miles. These waves are the so-called electro-magnetic waves. 

 Light, radiant heat, and electro-magnetic waves are all of the 

 same nature; they differ only as regards their wave-lengths. 



LIGHT VISIBLE AND INVISIBLE 



If Light, then, consists of waves transmitted through the 

 ether, what gives rise to the waves? Whatever sets up such won- 

 derfully rapid series of waves must be something with an enor- 

 mous vibration. We come back to the electron: all atoms of 

 matter, as we have seen, are made up of electrons revolving in a 

 regular orbit round a nucleus. These electrons may be affected 

 by out-side influences, they may be agitated and their speed or 

 vibration increased. 



