N. B. THE principal alterations in the second volume with respect to the first edition, beside its being made to begin with Mensuration of Solids, are the addition of Demonstrations in Notes to nearly all the Problems in Mensuration of Solids, and in Gauging, and of some Questions for practice at the end of Spheric Trigonometry; and the omission of two of the most complex and least useful Problems in Dialing.