THE idea of writing this Treatise suggested itself to me a considerable time since, from knowing the repeated inquiries that had been made for such a book; and after perusing, I believe, every work that has been published on the subject, I was fully convinced of the necessity of such a work, adapted to the present improved practice. Of the works on Surveying, I may say, they are all elementary, and of ante-date, no treatise, that I am aware of, having been published since the fine mathematical instruments at present in use have been considered a necessary adjunct to the successful prosecution of land surveying. Of the treatises published on levelling, there is only one of recent date, by Mr. Sims, that can be referred to, and I consider that does not supply the wants of persons seeking information on the subject.