SECT. I.

THE PROJECTS OF BRIDGES, &C.

is chiefly to be made, will naturally produce an article ofthe first consequence; and a great many others, if necessary,ought to be sacrificed to it. If possible, the bridge shouldbe placed where there can conveniently be opened and madepassages or streets from the end of it in every direction, andespecially one as nearly in the direction of the bridge itselfas possible, tending towards the body of the town, withoutnarrows or crooked windings, and easily communicatingwith the chief streets, thoroughfares, &c.—And here everyperson, in judging of this, should divest himself of all partialregards or attachments whatever; think and determine forthe good of the whole only, and for posterity as well as forthe present.

The banks or declivities towards the river are also of par-ticular concern, as they affect the conveniency of the passageto and from the bridge, or determine the height of it, onwhich in a great measure depends the expense, as well as theconvenience of passage. The breadth of the river, the na-vigation upon it, and the quantity of water to be passed, orthe velocity and depth of the stream, form also considera-tions of great moment; as they determine the bridge to behigher or lower, longer or shorter. However, in most cases,a wide part of the river ought rather to be chosen than a nar-row one, especially if it is subject to great tides or floods: for,the increased velocity of the stream in the narrow part, beingagain augmented by the further contraction of the breadth bvthe piers of the bridge, will both incommode the navigationthrough the arches, and undermine the piers and endangerthe whole bridge. The nature of the bed of the river is alsoof great concern, it having a great influence on the expense;as upon it, and the depth and velocity of the stream, dependthe manner of laying the foundations, and building the piers.These are the chief and capital articles of consideration,which will branch themselves out into other dependent ones,and so lead to the required estimate of the whole.

Having resolved on the place, the next considerations are,the form, the estimate of the expense, and the manner of