SCIENCE 



New Series 



VOL. LIV, No. 1407 



Friday, December 16, 1921 



Single Copies, 15 Cts. 

 Annual Subscription, $6.00 



Double Impression 

 on Growing Minds 



Get the students' interest and complete attention by 

 focusing those two receptive senses, sight and hearing, on 

 the one subject. Illustrate the lessons with pictures, en- 

 larged on a screen by the 



Bausch & Lomb 



BALOPTICON 



The Perfect Stereopticon 



The Balopticon is invaluable in the 

 class room and assembly hall. It projects 

 photographs, drawinfifs, maps, colored 

 prints, specimens, etc., as well as slides. 

 The perfect illumination and freedom from 

 trouble makes the Balopticon an elScient 

 assistant to the instructor. 



Write for more information. 



Bausch ^ Ipmb Optical (p. 



New York 



552 St. Paul Street 



Washington 



ROCHESTER, N. Y. 



San Francisco 



Chicago San Francisco London 



Leading American Makers of Photographic Lenses, Microscopes, Projection Apparatus 

 (Balopticoru), Ophthalmic Lenses and Unstrumen'SyPhotomicrographic Apparatus, Range 

 Finders and Gun Sights for Army and Navy, Searchlight Reflectors, Stereo-Prism 

 Binoculars, Magnifiers, and other high-grade Optical Products 



"^ that gesTmy see 



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-.^heitcr dnl farther -^^^^^^^^ 



