BRIDGE.
T.. mathematical theory of the structure of bridges has been a favourite subject with mecha nical philosophers ; it gives scope to some of the most refined and elegant applications of science to practical utility; and at the same time that its progressive improvement exhibits an example of the very slow steps by which speculation has sometimes followed execution, it enables us to look forwards with perfect confidence to that more desirable state of human knowledge, in which the calculations of the mathematician are authorised to direct the ope rations of the artificer with security, instead of watching with servility the progress of his labours.
Ot the origin of the art of building bridges a sketch has been given in the body of the Encyclol padia ; the subject has been rediscussed within the last twenty years by some of the most learned anti quaries, and of the most elegant scholars of the age; but additions still more important have been made to the scientific and practical principles on which that art depends ; and the principal inlbrmation, that is demanded on the present occasion, will be compre hended under the two heads of phyeico-mathematical principles, subservient to the theory of this depart ment of architecture, and a historical account of the works either actually executed or projected, which appear to be the most deserving of notice. The first
head will contain three sections, relating respective ly(1) to the resistance of the materials employed, (2) to the equilibrium of arches, and (3) to the effects of friction ; the second will comprehend (4) some de tails of earlier history and literature, (5) an Se camt of the discussions which have taken place re• specting the improvement of the port of London, and (6) a description of some of the most remark able bridges which have been erected in modem times.