SCIENCE 



''>S. 



New Series 

 VOL. LIV, No. 



Friday, October 21, 1921 



■"T^ 



Single Copies, IB Cts. 

 Annual subsckiption, $6.00 



^^Just remember that" 



you say to the pupil. Isn't it asking a lot of him — to displace ^ ?^ %^ nind 

 the impressions of things he has seen by those of which he has om^ - neard? 

 Show him the things he's trying to learn. Project them on a screen with a 



Bausch & Lomb 



BALOPTICON 



The Perfect Stereopticon 



Maps, illustrations, postcards, photographs — all in full colors can be shown. 

 There are also Balopticon models for showing slides alone, or both slides 

 and opaque subjects. The new gas-filled Mazda lamp gives brilliant and 

 safe illumination — and it runs itself. 



Bausch ^ Ipmb Optical (g. 



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ROCHESTER, N. Y. 



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Leading American Makers of Photographic Lenses, Microscopes, Projection Apparatus 

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