THE PRISMATIC SPECTRUM. 53 



bent about and decomposed by means of the 

 prism.] Now,, here you see, if I send the 

 light through this piece of plain glass. A, it 

 goes straight through, without being bent (un- 

 less the glass be held obliquely, and then the 

 phenomenon becomes more complicated), but 

 if I take this piece of glass, B [a prism], you 

 see it will show a very different effect. It no 

 longer goes to that wall, but it is bent to this 

 screen, c, and how much more beautiful it is 

 now [throwing the prismatic spectrum on the 

 screen]. This ray of light is bent out of its 

 course by the attraction of the glass upon it. 

 And you see I can turn and twist the rays to 

 and fro, in different parts of the room, just as 

 I please. Now it goes there, now here. [The 

 Lecturer projected the prismatic spectrum 

 about the theatre.] Here I have the rays 

 once more bent on to the screen, and you see 

 how wonderfully and beautifully that piece of 

 glass not only bends the light by virtue of its 

 attraction, but actually splits it up into diffe- 

 rent colours. Now, I want you to understand 

 that this piece of glass [the prism] being 

 perfectly uniform in its internal structure, tells 

 us about the action of these other bodies which 



E 3 



