TRACT I.

THE

PRINCIPLES OF BRIDGES:

CONTAINING

THE MATHEMATICAL DEMONSTRATION OF THE PROPERTIESOF THE ARCHES, THE THICKNESS OF THE PIERS, THE FORCEOF THE WATER AGAINST THEM, &C. WITH PRACTICAL OB-SERVATIONS AND DIRECTIONS DRAWN FROM THE WHOLE.

THIS Tract, on bridges, originated from the circumstanceof the fall of Newcastle bridge, in the year 1771; which,with other particulars relative to the Tract, are noticed inthe Preface to that Edition of it; which was as follows:

THE ORIGINAL PREFACE.

A large and elegant bridge, forming a way over a broadand rapid river, is justly esteemed one of the noblest piecesof mechanism that man is capable of performing. And theusefulness of an art which, at the same time that it connectsdistant shores by a way over the deep and rapid waters, alsoallows those waters and their navigation to pass smooth anduninterrupted, renders all probable attempts to advance thetheory or practice of it, highly deserving the encouragementof the public.

This little book is offered as an attempt towards the im-provement of the theory of this art, in which the more es-sential properties, dimensions, proportions, and other rela-TOL. I. B

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