STUDIES IN NATURE 



into heat, and their energy and strength goes to 

 raise the temperature of the absorbing body. 

 When the great ocean waves reach some ob- 

 stacle like the coast or islands of rock, we find 

 foam and confusion, breakers and noise ; in the 

 same way, when the waves of radiation strike 

 the particles of a body, those particles destroy 

 some of the ether waves, and are themselves set 

 into the mode of vibration which we know as 

 heat. 



We have not yet finished the history of these 

 ether waves, for not quite all the energy of the 

 absorbed waves is changed into heat. In the 

 chapter on Air, we saw that under the influence 

 of sunlight, green plants were able to decompose 

 carbonic acid and liberate oxygen. To do this 

 also requires energy, which the plants obtain 

 from the sun's radiation. Again, we know that 

 when falling on certain kinds of sensitive sur- 

 faces, light is able to produce obscure chemical 

 changes which result in a photograph. Here 

 again, some of the absorbed rays are used in 

 other ways than merely to heat the absorbing 

 body. The light that enters our eyes, and 

 through them gives impressions of shape, colour, 

 and shade to our brains, must have a very com- 

 plicated history, one that has not yet been traced 

 out fully. We cannot follow up all these different 

 possibilities here. We must be content for the 

 present to have learned a little about the nature 

 of this wonderful wave-motion. 



<6o) 



