21 OCTOBER 1899, Page 24

Of technical books on various subjects we have to mention

Optics, by A. S. Percival, M.B. (Macmillan and Co., 10s. net). Mr. Percival explains that he writes in the first place for students of ophthalmic medicine. It is obvious that the possession of the correct theory of sight is of the first importance to any one who seeks to correct the imperfections of the human organ.— Elements of Physics. By Henry Crew, Ph.D. (Same publishers, is.)—Billiards Mathematically Treated. By G. W. Hemming, Q.C. (Same publishers. 3s. 6d. net.)—Here again theory is called to assist practice. No one could be found better qualified :o expound theory than Mr. Hemming, who was Senior Wrangler m 1847.