The book has been prepared for young members of the profession ; and one of the leading objects has been to elucidate In plain Bngllsli a few Important elementary principles which the savants have enveloped In such a haze of mystery as to render pursuit hopeless to any but a confirmed mathematician. From preface to first edition of Trautwlne's Pocket Book. Pays well on Small Investment Stereopticons, Magic Lanterns, and Views illustrating every subject for public exhibitions. Lanterns for colleges, Sunday schools, and home amusements. 152 page illustrated catalogue free. McAllister, Manufacturing Optician, 49 Nassau St., N. T. All Books, App., etc. cheap. School of Electricity, N.Y. Wanted SCIENTIFIC AMERICAN, vol. 50, Nos. 4,16, and 18. Address C. A. M., SCIENTIFIC AMERICAN Office, New York. Steam jacketfeedwater boilerand purifier. New catalogue free. Wm. Baragwanath Son, 40 W. Division St., Chicago. Pedestal tenoner. All kinds woodworking machinery. C. B. Rogers Co., Norwich, Conn. Stationary and boat engines, boilers. Best and cheapest. 1 to 10 H. P. Washburn Engine Co., Medina, Ohio. For the latest improved diamond prospecting drills, address the M. C. Bullock Mfg. Co., 138 Jackson St., Chicago, 111. The Bailroad Gazette, handsomely illustrated, published weekly, at 73 Broadway, New York. Specimen copies free. Send for catalogue of railroad books. The Knowles Steam Pump Worlis, 113 Federal St.. Boston, and 93 Liberty St., New York, have just Issued a new catalogue, in which are many new and improved forms of Pumping Machinery of the single and duplex, steam and power type. This catalogue will be mailed free of charge on application. Link Belting and Wheels. Link Belt M. Co., Chicago. Presses Diea Ferracute Maeh. Co., Bridgeton, N. J Woodworking Machinery of all kinds. The Bentel Margedant Co.. Ue Fourth St., Hamilton, O. Nickel Plating. Sole manufacturers cast nickel anodes, pure nickel salts, polishing compositions, etc. 100 "lAttUWander." A perfect Electro Plating Machine. Sole manufacturers of the new Dip Lacquer Kristaline. Complete outfit for plating, etc. Hanson, Van Winkle Co., Newark, N. J., and 92 and ? Liberty St., New York. Supplement Catalogne. Persons In pursuit of information of any special engineering, mechanical, or ?? ?-tifio subject, can have catalogue of contents of the Sci- NTiPic AMERICAN SUPPLEMENT sent to them free. The SUPPLEMENT contains lengthy articles emoracing the whole range of engineering, mechanics, and physical clence. Address Munn Co., Publishers, New York. Iron Planer, Lathe, Drill, and other machine tools of modem design. NewHaTenMfg.Co.,NewIIaven,Conn. Iron, Steel, and Copper Drop Forgings of every description. Billings Spencer Co., Hartford, Conn. 60,000 Bmersont 188? VW Book of superior saws, with Supplement, sent free to all Sawyers and Lumbermen. Address Dmerson, Smith Co., Limited, Beaver Falls, Pa., U. S. A. Pat. Geared Scroll Chucks, withS pinions, sold at same pflces as common chucks by Cushman Chuck Co., Hartford, Conn. Steam Hammers, Improved Hydraulic Jacks, and Tube Expanders. R. Dudgeon, 24 Columbia St., New York. The best Dynamoatox Light, for Nickel Plating, Elec-trotyping, etc., are made and warranted by the Excelsior Electric Co., New York. Send for catalogue. Hoisting Engines, Friction Clutch Pulleys, Cut-off Couplings. D. Frisbie Co 112 Liberty St., New York. "How to Keep Boilers Clean." Send your address for free 88 page book. Jas.C. Hotchkiss, 120 Liberty St., N.Y. The Holly Manufacturing Co., of Lockport, N. Y., will send their pamphlet, describing water works machinery, and containing reports of tests, on application. Durrell's imp. nut tapper. Taps to 2 in. New imp. bolt cutter. Howard Bros., Iron Works, Fredonia, N. Y. For best leather belting and lace leather, including Hercules, see Page Belting Co.'s adv., p. 173. Double boring machinea Double spindle shaping machines. Rollstone Machine Co., Fltchburg, Mass. Split Pulleys at low prices, and of same strength and appearance as Whole Pulleys. Yocom Son's Shafting Works, Drinker St., Philadelphia, Pa. Send for new and complete catalogue of Scientific Books for sale by Munn 4 Co., 361 Broadway, N. Y. Free on application.