CH. xxn. SUMMARY. 185 



careful study of the laws of light. This it was which caused 

 Snellius to make experiments on the bending of rays with a 

 view to improving telescopes, and so to discover the law of 

 refraction, afterwards more fully stated by Descartes. Then 

 we find this last philosopher trying to explain the rainbow, 

 and studying the colours falling through a prism, and so the 

 subject passed on into the hands of Newton. 



Here, by experiment again, the threads of light were dis- 

 entangled in the prism, and Newton drew out its many- 

 coloured rays, tracing them one by one on their road, till he 

 had shown that refraction explained them, and that to this 

 law, which seemed so uninteresting at first, we owe all the 

 lovely colours which surround us. And now Huyghens 

 takes up the story and leads us fairly into the invisible 

 world. This light, which Roemer had proved to be travel- 

 ling across space with marvellous speed, Huyghens shows 

 to be no actual substance at all, but most probably a 

 trembling of an invisible and intangible ether a succession 

 of infinitely tiny waves chasing each other across millions of 

 miles, and striking at last on the minute opening of our eye, 

 bringing to us the wonderful effects of light. As Newton 

 traced colours, so Huyghens traces the invisible waves through 

 many substances, showing us their path and why they take 

 it ; and landing us at last in the bewildering effects of polar- 

 ization, leaves us there to wait for more knowledge in a 

 future century. 



Biology. And now we come to Biology, or the study of 

 all those sciences which relate to life. Here you must re- 

 member that our account of the discoveries made, must be 

 more than usually imperfect, because the subject is more than 

 usually difficult. Yet we can form some idea of the new 

 light thrown upon the nature of the living body, by Harvey's 



