rning-glass is fixed over the cannon in such a manner that
when the sun comes to the meridian--which it does every day at noon,
you know--its rays are concentrated on the touch-hole, and of course
the powder is ignited and the cannon is fired.

Most boys understand the power of a burning-glass, and know how easily
dry grass or tinder, or a piece of paper, may be set on fire by a good
glass when the sun is bright; but they would find it very difficult to
place a glass over a little cannon so that it would infallibly be
discharged at any set hour. And even if they could do it, they would
not be sure of their cannon-clock being _exactly_ right, for the sun
does not keep the very best time. He varies a little, and there is a
difference between solar time and true time. But the sun is always
near enough right for all ordinary intents and purposes.

I know boys--lazy fellows--and some girls of the same sort, for that
matter,--who, if they could, would have, just outside of their
school-doors, one of the largest cannon, which should go off every day
at the very earliest hour at which school would let out, and which
should make such a tremendous report that it would be impossible for
the teacher to overlook the time and keep them in too long.

But if these same boys and girls were putting up a cannon to go off at
the hour when school commenced, they would get such a little one that
it wouldn't frighten a mouse.

WATERS, DEEP AND SHALLOW.

With such a vast subject before us as the waters of our beautiful
world, we must be systematic. So we will at first confine ourselves to
the observation of _pleasant waters_.

[Illustration]

Let us begin at the beginning.

This pretty little spring, with its cool water running day and night
into the old barrel, and then gurgling over the staves, flowing away
among the grass and flowers, is but a trifling thing perhaps, and
might be passed with but little notice by people who have always lived
in cities. But country-folks know how to value a cool, unfailing
spring. In the hot days of summer the thirsty and tired farmer would
rather see that spring than an ice-cream saloon. Yes, even if he has
nothing to drink from but a gourd, which may be lying there among the
stones. He may have a tin-cup with him,--and how shocking! he may
drink out of his hands! But, let him use what he may, he certainly
gets a most delicious drink.

I once knew a little girl who said she could not bear