should give out an enormous quantity of light and heat; so
enormous that it is almost impossible to form any idea of it.
Sir John Herschel has, indeed, tried to picture it for us. He
found that a ball of lime with a flame of oxygen and hydrogen
playing round it (such as we use in magic lanterns and call oxy-
hydrogen light) becomes so violently hot that it gives the most
brilliant artificial light we can get - such that you cannot put
your eye near it without injury. Yet if you wanted to have a
light as strong as that of our sun, it would not be enough to
make such a lime-ball as big as the sun is. No, you must make it
as big as 146 suns, or more than 146,000,000 times as big as our
earth, in order to get the right amount of light. Then you would
have a tolerably good artificial sun; for we know that the body
of the sun gives out an intense white light, just as the lime-
ball does, and that , like it, it has an atmosphere of glowing
gases round it.

But perhaps we get the best idea of the mighty heat and light of
the sun by remembering how few of the rays which dart out on all
sides from this fiery ball can reach our tiny globe, and yet how
powerful they are. Look at the globe of a lamp in the middle of
the room, and see how its light pours out on all sides and into
every corner; then take a grain of mustard-seed, which will very
well represent the comparative size of our earth, and hold it up
at a distance from the lamp. How very few of all those rays
which are filling the room fall on the little mustard-seed, and
just so few does our earth catch of the rays which dart out from
the sun. And yet this small quantity (1/2000-millionth part of
the whole) does nearly all the work of our world. (These and the
preceding numerical statements will be found worked out in Sir J.