Herschel's 'Familiar Lectures on Scientific Subjects,' 1868, from
which many of the facts in the first part of the lecture are
taken.)

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
sold, 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 intense heat and make the air cool and pleasant
for us.



Week 4

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 with to touch you from this platform where I stand,
I can do it in two ways. Firstly, I can throw something at you