until, about a hundred years ago,
Sir Humphry Davy noticed something which other people had not
observed. He discovered that flame would not pass through fine wire
gauze, and he made a safety lamp in which a little oil lamp was placed
in a round funnel of wire gauze. The light, but not the flame, would
pass through it; and all safety lamps that burn oil have been made on
this principle. The electric lamp, however, is now in general use. The
miner wears it on his cap, and between his shoulders he carries a
small, light storage battery. Even with safety lamps, however, there
are sometimes explosions. The only way to make a mine at all safe from
dangerous gases is to keep it full of fresh, pure air. There is no
wind to blow through the chambers and passages, and therefore air has
to be forced in. One way is to keep a large fire at the bottom of the
air shaft. If you stand on a stepladder, you will feel that the top of
the room is much warmer than the floor. This is because hot air
rises; and in a mine, the hot air over the fire rises and sucks the
foul air and gas out of the mine, and fresh air rushes in to take its
place. Another way is by a "fan," a machine that forces fresh air into
the mine.

[Illustration: MINERS AND THEIR MINE

Notice the safety lamps in the men's caps, and the little railroad on
which the cars of coal and ore travel, hauled by the useful mule.]

So it is that by hard work and much danger we get coal for burning.
Now, coal is dirty and heavy. A coal fire is hard to kindle and hard
to put out, and the ashes are decidedly disagreeable to handle. And
after all, we do not really burn the coal itself, but only the gas
from it which results from the union of carbon and oxygen. In some
places natural gas, as it is called, which comes directly from some
storehouse in the ground, is used in stoves and furnaces and
fireplaces for both heating and cooking; and perhaps before long gas
will be manufactured so cheaply and can be used so safely and
comfortably that we shall not have to burn coal at all, but can use
gas for all purposes--unless electricity should take its place.

II

DOWN IN THE QUARRIES

When walking in the country one day I came to a beautiful pond by the
side of the road. The water was almost as clear as air, and as I
looked down into it, I could see that the bottom was made of granite.
The farther shores were cliffs of clean granite thirty or forty feet
high and coming down to th