i88o.J 
On Water and Air. 
61 
light some coloured glasses. Here I have a green glass* 
Well, you see that now the light on the screen is green. Here 
I have a blue glass, and that causes the light to be blue ; and 
here I have a red glass, and that causes it to be red. What 
I want you to understand is that the blue and the green and 
the red are all in that white light. And now I want to pull 
those distinct colours one from the other. I want to 
separate the colours which produce that white light. I do 
that by sending the light through a body of a certain shape, 
which is called a prism. We will cause the light to pass 
through it. |The experiment was performed, and the usual 
spedbrum appeared on the screen.] Is not it lovely? I 
have seen it a great many times, but never without wonder 
at its beauty. But now I want to make that longer. I will 
send the light through another prism. Here it is. You 
will observe that by using this other prism I can manage to 
make my coloured image a great deal longer. This coloured 
image which I obtain by sending the light through the 
prisms is called the spedbrum ; and the great Sir Isaac 
Newton proved that the slice of white light that you saw a 
moment ago upon the screen has contained in it all that 
numerous mass of colours which appear in the spedbrum. 
Now, I wish that I had a ruddy faced boy that I might 
cause him to pass through that spedbrum. You would find 
his ruddiness varied very much in passing through the 
various colours. I want to bring before you the fadb that 
the colour of a body is owing to the colour which it throws 
back to the eye. Take a rose. When the white light of the 
sun falls upon the rose, it enters the rose some depth, but, 
as it is ejedbed again from the rose, certain colours are 
quenched, and certain colours are sent back to the eye, and 
the colour of the rose is due to the colours sent back to the 
eve. 
Why was the red glass red ? Because it quenched the 
other colours, and allowed only the red to pass. And what 
is true of red glass is true of red cloth, or of any other 
colour. Now, I want to show you that these colours are 
thus quenched. Here I have a beautiful piece of red cloth. 
It is now vividly red in the red light of the spedbrum. But 
why is this red cloth red ? It is because it quenches the 
other colours, and sends the red colour back to the eye. If 
we pass it on to the green part of the spedbrum it will send 
back no colour to the eye, and there it is black.. Again, we 
will take the opposite experiment. Here is a piece of green 
silk. The green silk is green because it quenches all the 
other colours except green, and sends the green colour back 
