BACK NUMBER—Complete seta of the present volume of tho SCIBNTIFIO AHKILIOA ean yet be fnrniahed at the subscription price. PAINT CIIMS—Persona desiring the claim of any Invention which has been patented within fourteen years, ean obtain a copy by addressing a letter lo this office, stating the name of the patentee, and date of patent when known, and enclosing $1 as fee for copy-Ing. RECEIPT—When money la paid at the office for sub-Bcrlptiona, a receipt for it will always be given; bui when snbseiibera remit their money by mail, they may consider the arrival of the flrat paper a buna fide acknowledgment of the reeelpt of their funds. The Post Offlec law doea not allow publishers to enclose receipts In the paper.Terms of Advertising Twenty-five cents per lino each insertion. Werc-peotfully request that our patrons will make their advertisements as ahort as possible. Engravings cannc* be admitted Into the advertising columns. %* All advertisements must be paid for before in* Berfelng. SAMUEL MeELROY, CIVIL ENGINEER— Late U. S. Naval and Civil Engineer. Speeial attention paid to water-works with pumping power. Address "Engineer's Offiee," Wat-er-works, Brooklyn, Long Inland. TO CONSUMERS OF ALUM —POCHIN'S Patent Aluminous Cake, as a eubstitutefor alum, U rapidly taking the plaoe of alum, both in England and this country. The price per ponndti about the same as alum, while the cake is 25 per cent stronger. Circulars witn full particulara can be had on application to J. B. SHEFFIELD* CO., Bole Agenta for the United States and Canada, 65 and 63 Beekman at, New York. THE WORKS OF THE AUBIN GAS CO., (General Office, No. 44 State at., Albany, N. Y.,) as now perfected, are adapted to all materials and localities, and are in aneceBpful operation in villages, factories, and private dwellings. For full information as to cost, proljable income ot public works, , apply as above. For plane, c., see SCIENTIFIC AMERICAN of March 13th. "I?IiECTmCAL APPARATUS-ON RECEIPT X-i of 26 eenta, I will sendf ulldlrections formakinj a cheap and simple apparatus, capable of giving strons shocks. Materials can be found anywhere, and can be made by anybody. Addret AMOS J. BOOT, Medina, Medina eo,, Ohio.