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 (unless 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 different 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
