If opportunity should occur to the reader to visit a large ship-building establishment, such as those on any one of the five rivers named above, he will see something like the following routine of operation going on:-- There is, first, the 'ship's draughtsman,' whose duties are somewhat analogous to those of the architect of a house, or the engineer of a railway, or the scientific cutter at a fashionable tailor's: he has to shape the materials out of which the structure is to be built up, or at least he has to shew others how it is to be done. When the ship-builder has received an order, we will say, to construct a ship, and has ascertained for what route, and for what purpose, and of what size it is to be, he and his ship's draughtsman 'lay their heads together' to devise such an arrangement of timbers as will meet the requirements of the case. Here it is that a _science_ of ship-building would be valuable; the practical rules followed are deductions not so much from general principles as from accumulated facts which are waiting to be systematised; and until this process has been carried further, ship-building will be an _art_, but not a _science_. Well, then; the draughtsman, gathering up all the crumbs of knowledge obtainable from various quarters, puts his wisdom upon paper in the form of drawings and diagrams, to represent not only the dimensions of the vessel, but the sizes and shapes of the principal timbers which are to form it, on the scale, perhaps, of a quarter of an inch to a foot. Then this very responsible personage goes to his 'mould-loft,' on the wide-spreading floor of which he chalks such a labyrinth of lines as bewilder one even to look at. These lines represent the actual sizes and shapes of the different parts of the ship, with curvatures and taperings of singularly varied character. One floor of one room thus contains full-sized contours of all the timbers for the ship. So far, then, the draughtsman. Next, under his supervision, thin planks of deal are cut to the contours of all these chalk-lines; and these thin pieces, called _moulds_, are intended to guide the sawyers in cutting the timbers for the ship. A large East Indiaman requires more than a hundred mould-pieces, chalked and marked in every direction.