Fa. But do you suppose he can do this as a common carpenter makes a box or set of shelves?

Ch. I do not know.

Fa. Do you not think that such a vast bulk requires a good deal of contrivance to bring it into shape, and fit it for all its purposes?

Ch. Yes.

Fa. Some ships, you have heard, sail quicker than others-some bear storms better-some carry more lading-some draw less water-and so on.

not suppose

chance? Ch. No.

You do all these things are left to

Fa. In order with certainty to produce these effects, it is necessary to study proportions very exactly, and to lay down an accurate scale by mathematical lines and figures after which to build the ship. Much has been written upon this subject, and nice calcula

tions have been made of the resistance a ship meets with in making way through the water, and the best means of overcoming it; also of the action of the wind on the sails, and their action in pushing on the ship by means of the All these must be understood

masts.

by a perfect master of ship-building. Ch. But I think I know ship-builders who have never had an education to fit them for understanding these things.

Fa. Very likely; but they have followed by rote the rules laid down by others; and as they work merely by imitation, they cannot alter or improve as occasion may require. Then, though common merchant-ships are trusted to such builders, yet in constructing men of war and Indiamen, persons of science are always employed. The French, however, attend to this matter more than we do, and in conse

quence, their ships generally sail better

than ours.

Ch. But need a captain of a ship know all these things?

Fa. It may not be absolutely necessary; yet occasions may frequently arise in which it would be of great advantage for him to be able to judge and give direction in these matters. But suppose the ship built-what comes next? Ch. I think she must be rigged.

Fa. Well--who are employed for this purpose?

Ch. Mast-makers, rope-makers, sailmakers, and I know not how many other people.

;

Fa. These are all mechanical trades and though in carrying them on much ingenuity has been applied in the invention of machines and tools, yet we will not stop to consider them. Suppose her, then, rigged-what next?

Ch. She must take in her guns and powder.

Fa. Stop there, and reflect how many arts you have now set to work. Gunpowder is one of the greatest inventions of modern times, and what has given such a superiority to civilized nations over the barbarous. An English frigate, surrounded by the canoes of all the savages in the world, would easily beat them off by means of her guns; and if Cæsar were to come again to England with his fleet, a battery of cannon would sink all his ships, and set his legions a swimming 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?

Fa. It comprehends the knowledge of all the properties of metals and minerals, salts, sulphur, oils, and gums,

VOL. I.

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 three 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 chemical experiments, and many more experiments have been employed to bring it to perfection.

Ch. But need a captain know how to make gunpowder 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