AND THE THEORY OF LIGHT. 13 



arguments in support of tlie explanation of it, it was 

 almost impossible to resist the conviction, that shadow 

 must perform a most important part in the formation of 

 colour, and take its place in every theory of colour. 



2 1 . But how is this to be proved ? 



No one can study light at present without at the same 

 time studying the theory of Newton, and Newton has 

 attempted to prove the very reverse. He has completely 

 abolished shadow from his theory of colour. For, after 

 having reflected, as he says, the various colours of the 

 prism on the "confines of shadow," he concludes "that 

 all colours have themselves indifferently to any confines 

 of shadow, and therefore the difl'erences of these colours 

 from one another do not arise from the difierent confines 

 of shadow whereby light is variously modified, as has 

 hitherto been the opinion of philosophers." This is 

 quite decided. But so is our experiment. The above 

 experiment tells us, that a force which produces red when 

 red is seen by itself, no longer produces red but green, 

 brown, or some other colour, as the case may be, when 

 the red is seen alternately with black or shadow.* I use 

 shadow in Newton's acceptation of the word, and in that 

 of the ancients ; I shall use it in a modified sense by and 



by. 



22. Newton's arguments are drawn from the experi- 

 ments which he made with the prism. But the phenomena 

 of the prism, being so difficult of explanation and com- 

 plex, should be compared with other phenomena of a 

 more simple kind, and not with changes perpetually rung 

 upon itself. Such a method of experimenting seems to 



* I name these various colours as the effect is not constant but depends 

 much on the state of the atmosphere. And this is not to be wondered 

 at in this instance, where there is a physical difSculty in making the experi- 

 ment, since Sir John Herschel says, and every one who has experimented 

 can verify what he says, that the image of the sun produced by the prism 

 "varies enormouslv." 



