SUNBEAMS AND THEIR WORK. 33 
In order to see how powerful the sun's rays are, 
you have only to take a magnifying glass and gather 
them to a point on a piece of brown paper, for they 
will set the paper alight. Sir John Herschel tells us 
that at the Cape of Good Hope the heat was even 
so great that he cooked a beefsteak and roasted some 
eggs by merely putting them in the sun, in a box 
with a glass lid ! Indeed, just as we should all be 
frozen to death if the sun were cold, so we should 
all be burnt up with intolerable heat if his fierce rays 
fell with all their might upon us. But we have an 
invisible veil protecting us, made of what do you 
think? Of those tiny particles of water which the 
sunbeams draw up and scatter in the air, and which, 
as we shall see in Lecture IV, cut off part of the in- 
tense heat and make the air cool and pleasant for us. 
We have now learnt something of the distance, the 
size, the light, and the heat of the sun the great 
source of the sunbeams. But we are as yet no nearer 
the answer to the question, What is a sunbeam? how 
does the sun touch our earth? 
Now suppose I wish to touch you from this plat- 
form where I stand, I can do it in two ways. Firstly, 
I can throw something at you and hit you in this 
case a thing will have passed across the space from 
me to you. Or, secondly, if I could make a violent 
movement so as to shake the floor of the room, you 
would feel a quivering motion ; and so I should touch 
you across the whole distance of the room. But in 
this case no thing would have passed from me to you 
but a movement or wave, which passed along the 
