Produced by Leonard D Johnson, Juliet Sutherland and the Online Distributed Proofreading Team at http://www.pgdp.net [Illustration: Issue Title.] SCIENTIFIC AMERICAN A WEEKLY JOURNAL OF PRACTICAL INFORMATION, ART, SCIENCE, MECHANICS, CHEMISTRY, AND MANUFACTURES. NEW YORK, MARCH 29, 1879. Vol. XL., No. 13. [NEW SERIES.] $3.20 PER ANNUM. [POSTAGE PREPAID.] * * * * * SCIENTIFIC AMERICAN. ESTABLISHED 1845. MUNN & CO., Editors and Proprietors. PUBLISHED WEEKLY AT NO. 37 PARK ROW, NEW YORK. O. D. MUNN. A. E. BEACH. TERMS FOR THE SCIENTIFIC AMERICAN. One copy, one year, postage included $3 20 One copy, six months, postage included 1 60 CLUBS.--One extra copy of THE SCIENTIFIC AMERICAN will be supplied gratis for every club of five subscribers at $3.20 each; additional copies at same proportionate rate. Postage prepaid. Single copies of any desired number of the SUPPLEMENT sent to one address on receipt of 10 cents. Remit by postal order. Address MUNN & CO., 37 Park Row, New York. THE SCIENTIFIC AMERICAN SUPPLEMENT is a distinct paper from the SCIENTIFIC AMERICAN. THE SUPPLEMENT is issued weekly. Every number contains 16 octavo pages, with handsome cover, uniform in size with SCIENTIFIC AMERICAN. Terms of subscription for SUPPLEMENT, $5.00 a year, postage paid, to subscribers. Single copies 10 cents. Sold by all news dealers throughout the country. COMBINED RATES.--The SCIENTIFIC AMERICAN and SUPPLEMENT will be sent for one year, postage free, on receipt of _seven dollars_. Both papers to one address or different addresses, as desired. The safest way to remit is by draft, postal order, or registered letter. ADDRESS MUNN & CO., 37 PARK ROW, N. Y. SCIENTIFIC AMERICAN EXPORT EDITION. The SCIENTIFIC AMERICAN Export Edition is a large and splendid periodical, issued once a month. Each number contains about one hundred large quarto pages, profusely illustrated, embracing: (1.) Most of the plates and pages of the four preceding weekly issues of the SCIENTIFIC AMERICAN, with its splendid engravings and valuable information; (2.) Commercial, trade, and manufacturing announcements of leading houses. Terms for Export Edition, $5.00 a year, sent prepaid to any part of the world. Single copies 50 cents. Manufacturers and others who desire to secure foreign trade may have large, and handsomely displayed announcements published in this edition at a very moderate cost. The SCIENTIFIC AMERICAN Export Edition has a large guaranteed circulation in all commercial places throughout the world. Address MUNN & CO., 37 Park Row, New York. VOL. XL., NO. 13. [NEW SERIES.] _THIRTY-FOURTH YEAR_. NEW YORK, SATURDAY, MARCH 29, 1879. * * * * * CONTENTS. (Illustrated articles are marked with an asterisk.)