"f^" 1 1905 



SCIENCE 



New Series. 

 Vol. XXI. No. 5s 



a. 



^Friday, March 31, 1905. 



Single Copies, 15 Cts. 

 Annual Subscription, 85.00. 





DUTY FREE 

 IMPORTA TION 



We import scientific instruments free of duty for col- 

 leges and universities from Societe Gene'voise, Cam- 

 bridge Scientific Instrument Co., Max Kohl, Carl Zeiss 

 Optical Works, Dr. M. Th. Edelmann, Otto Wolff, 

 Hartmann & Braun, Siemens & Halske, and many other sources. 



We shall endeavor to secure your business on the basis of moderate prices and to 

 keep it on the score of good service. An inquiry ivill receive a prompt reply. 



THE SCIENTIFIC SHOP albert b. porter 

 SCIENTIFIC INSTRUMENTS 322 Dearborn Street, CHICAGO 



Two Books Indispensable to Electricians 



By HENRY M. HOBART 



Electric Motors 



Continuous Current Motors 

 and Induction Motors, Their 

 1 heory and Construction. 



458 pp., 8vo, illustrated, $5. 



"Readable, useful, and indispensable to elec- 

 trical engineers who are working along the same 

 lines." 



— Engineering News. 



"Probably the most complete and advanced 

 treatise on electric motors yet published." 



— Electrical Review. 



" Far and away ahead of anything thus far 

 published in English on the subject.'' 



— Amer. Elfctrtcian . 



By TURNER & HOBART 



The Insulation of 

 Electric Machines 



By HARRY WINTHROP TURNER, 



Associate A. 1. E. E. and 



HENRY METCALF HOBART, 



M. I. E. E., Mem. A. I. E. E. 

 With 162 Illustrations. 



The results of twenty years of practical work 

 with insulating materials, and of careful study of 

 their insulating properties. Probably no other 

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 are so indefinite as these. 



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



