PREFACE.

Having been, for a long series of years, in the constanthabit of preserving original Tracts and dissertations on sci-entific subjects; and now enjoying, at a very advanced pe-riod of life, some degree of leisure, in consequence of myretirement from the laborious duties of the Royal MilitaryAcademy; I have anxiously embraced the opportunity ofselecting, and revising, such of those papers as were likelyto be most useful, and of presenting them to the public.

Some few parts of these Tracts have been already printedin the Philosophical Transactions, and in other works; butmost of them are quite new; and such as are not so, havingbeen recast and greatly improved, may be also consideredin some measure as original compositions. These papers,being necessarily of a miscellaneous nature, are here arrangednearly according to the order of time in which they werecomposed; and the description of them, is briefly as fol-lows.

volume i.

Tract I, is on the Principles of Bridges.—The original ofthis paper was a small pamphlet on the same subject, first pub-blished by me on a particular occasion at Newcastle, in theyear 1772. It was also republished at London in 1801, nearlyin the same state. But it has been now recomposed, andgreatly enlarged with marry additional propositions, as alsonumerous observations, both practical and scientific.

An Appendix is also added, containing my report to theCommittee of Parliament on the project for a new iron