The autotype of the twenty — five inch refractor is the gift of my friend Mr. Newall, and I take this opportunity of expressing my obligation to him, as also to Messrs. Cooke, Grubb and Browning for several of the woodcuts with which the chapters on the Equatorial are illustrated; and to Mr. H. Dent Gardner for some of those illustrating Clock and Chronometer Escapements, and for revising my account of them.