108 EIGHTH EVENING.

would sink all his ships, and set his legions a-swim-
ming in the sea. But the making of gunpowder, and
the casting of cannon, are arts that require an exact
knowledge of the science of chemistry.

Ch. What is that ?

a, It comprehends the knowledge of all the pro-
perties of metals and minerals, salts, sulphur, oils, and
gums, and of the action of fire, and water, and air upon
all substances, and the effects of mixing different
things together. Gunpowder is a mixture of threc
things only—saltpetre or nitre, sulphur or brimstone,
and charcoal. But who could have thought such a
wonderful effect would have been produced by it?

Ch. Was it not first discovered by accident ?

fa. Yes—but it was by one who was making che-
mical experiments, and many more experiments have
been employed to bring it to perfection.

Ch. But need a captain know how to make gun-
powder and cannon?

fa. It is not necessary, though it may often be
useful to him. However, it is quite necessary that he
should know how to employ them. Now the sciences
of gunnery and fortification depend entirely upon
mathematical principles; for by these are calculated
the direction of a ball through the air, the distance it
will reach to, and the force with which it will striko
anything. All engineers, therefore, must be FOOL
mathematicians.

Oh, But I think I have heard of gunners velug
httle better than the common men.

fa, ‘True—there is a way of doing that business,
as well as many others, by mere practice; and an
uneducated man may acquire skill in pointing a cau-
‘hon, as well as in shooting with a common sun. But
this is only in ordinary cases, and an abler head js
required to direct. Well—now Suppose your ship
conmletely fitted out for sea, and the wind blowing
fair; how will you navigate her ?

Ch Iwould spread the sails, and steer by the rudder,