JAN 9 



SCIENCE 



New Series. Q^I ,~^^^t^ TTuTnAv Tamttat?v Pi 1001^ Single Copies, 15 Cts. 



Vol. XXI. No. 523. Q o \ ' -CKIUAY, JAiNUAKY U, lV\JO. Annual Subscription, 85.00 



HARTMAN 8z: BRAUN '^^^SaSy"''' 



received a GRAND PRIZE at St. Louis for the excellence of their ELECTRICAL MEASURING INSTRUMENTS. 

 The apparatus which they make is specially suited for exacting laboratory work and is used, already, to a large 

 extent in American Universities and Colleges. 



As special U. S. agent I will send copy of their ILLUSTRATED CATALOGUE to any interested physicist 

 or electrical engineer who mentions this ad. 



JAMES G. BIDDLE, UU Chestnut St., Philadelphia 



Special Agent for: Weston Electrical Instrument Co., Roentgen Mfg. Co., Electric Storage Battery Co., 

 Hartmann & Braun, Siemens & Halske, Otto Woltf, Soci^te Genevoise, Max Kohl, Emil Gundelach, M. Th. Edel- 

 mann, Cambridge Scientific Instrument Co., Nalder Brost & Co., Kelvin .James White, Ltd., etc. 



SHaLER-DaVIS-HARRlS Models and Photographs 



aRE JUST THE THING 



for teaching physical geography, physiography and surface geology. Send for circular, 

 also for new price list of METEORITES (free). 



WARD'S NATURAL SCIENCE ESTABLISHMENT, 76-104 College Ave., Rochester. N. Y. 



jMiiii ■iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiii: 



[ HppHRarus for the Study ©f Raoio^HeTiviTY I 



; We are making our own model of Dolezalek Electrometer as recommended by Rutherford - 



z and other authorities ; also a full line of accessory apparatus. Write for circular. i 



E Headquarters for ELEeTRIS PREGISION aPPaRRTUS 0F aLL KINDS I 



i GauvaNOMETERS, eoivoBivsERS, RESisraiveE sxaivDaROs, = 



I P0TEIVTI0METERS, Etc., Etc. E 



i We make a full line of Induction Coils for all purposes. • s 



i American Agents for FLEUSS MECHANICAL AIR PUMPS 1 



= THE WILLYOUNG & GIBSON CO., 40 West Thirteenth Street, New York City | 



niiiiiiiiiiiiiiiiiiiiiiiiiiniiiMiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiir 



Testing of Electro-Magnetic IVIachinery 

 and other Apparatus ^ 



O BE COMPLETE IN TWO 

 VOLUMES 



By BERNARD VICTOR SWENSON and BUDD FRANKENFIELD 



University of Wisconsin. Nernst Lamp Company. 



Volume I. Cloth, 8vo. $3.00 net (postage 18c.). 



The field covered by the present volume is that of direct-current electro- magnetic machinery 

 and apparatus, and the book is almost exclusively confiued to dynamo-electric machinery. The 

 text refers in numerous places to various books and publications so as to make the hook serviceable 

 in connection with any first-class college course. This also adds to its value as a reference book. 

 Volume II., in preparation, will deal with alternating-current machinery, etc. 



THE MACMILLAN COMPANY, Publishers, 66 Fifth Ave., N. Y. 



