These different lines are extremely useful in exhibiting the various curves of a ship’s bottom, that as they are gradually diminished, their uniformity or irregularity may be discovered by the skilful artist. We have already observed, that the qualities required in a ship ought to determine the figure of the bottom: a ship of war therefore should be able to sail swiftly, and carry her lower tier of guns sufficiently out of the water. A merchant-ship ought to contain a large cargo of merchant-goods, and be navigated with few hands; and both should be able to carry sail firmly; steer well; drive little to leeward; and sustain the shocks of the sea without being violently strained. The first thing to be established in the draught of a ship is her length; and as a ship of war, according to her rate, is furnished with a certain number of cannon, which are placed in battery on her decks, it is necessary that a sufficient distance should be left between their ports to work the guns with facility, and particularly to leave space enough between the foremost gun and the stem, and between the aftmost gun and the stern-post on each side, on account of the arching, or inward curve of the ship towards her extremities. When the length of a ship is determined, it is usual to fix her breadth by the dimensions of the midship-beam. On this occasion the shipwrights, for the most part, are conducted by rules founded on their own observation; for having remarked, that some vessels which by repeated experience have been found to answer all the purposes of navigation, have a certain breadth in proportion to their length, they have inferred that it would be improper to depart from this proportion: but as other ships have been constructed with different breadths, which were equally perfect, a variety of different general rules have been adopted by these artists, who are accordingly divided in their opinions about the breadth which ought to be assigned to a ship relatively with her length, whilst each one produces reasons and experience in support of his own standard. Those who would diminish the breadth alledge, that a narrow vessel meets with less resistance in passing through the water; 2dly. That by increasing the length she will drive less to leeward; 3dly. That according to this principle, the water-lines will be more conveniently formed to divide the fluid; 4thly. That a long and narrow ship will require less sail to advance swiftly; that her masts will be lower, and her rigging lighter; and, by consequence, the seamen less fatigued with managing the sails, &c.