SUNBEAMS AND THEIR WORK. 
always make us see coloured light? Because, unless 
they are interfered with, they all travel along together, 
and you know that all colours mixed together in 
proper proportion, make white. 
I have here a round piece of cardboard, painted 
with the seven colours in succession several times over. 
When it is still you can distinguish them all apart, but 
when I whirl it quickly round see ! the cardboard 
looks quite white, because we see them all so instan- 
taneously that they are mingled together. In the same 
way light looks white to you, because all the differ- 
ent coloured waves strike on your eye at once. You 
can easily make one of these cards for yourselves, 
only the white will always look dirty, because you 
cannot get the col- 
ours pure. 
Now, when the 
light passes through 
the three-sided glass 
or prism, the waves 
are spread out, and 
the slow, heavy, red 
waves lag behind and 
remain at the lower 
end R of the coloured 
line on the wall (Fig. 
7), while the rapid 
little violet waves are 
bent more out of their road and run to V at the farther 
end of the line ; and the orange, yellow, green, blue, 
and indigo arrange themselves between, according to 
the size of their waves. 
FIG. 8. A, cardboard painted with 
the seven colours in succession ; 
B, same cardboard spun quickly 
round. 
