CffR 20 1922 



SCIENCE 



'P<^n3]3^0^ 



New Series 



Vol. LV, No. 1416 



Friday, February 17, 1922 



Single Copies, 15 Cts. 

 Annual Subscription, $6.00 



The Mental Camera 



THE iiiiiid is far more efficient 

 ill pliotograpliing pictures than 

 in recording spoken or printed in- 

 formation. To simplify instruc- 

 tion and make lasting impressions, 

 illustrate your talks with pictures, 

 enlarged on a screen by the 



BAUSGH & LOME 

 BALOPTICON 



The Perfect Stereopticon 



The Balopticon projects any kind of pictures, whether 

 on slides, post cards or in books — also specimens and other 

 opaque subjects. For strength, efficiency and ease of opera- 

 tion insist on a Balopticon. With gas-filled Mazda lamp it 

 almost runs itself. 



IVrite for detailed information and suggestions for using. 



BAUSGH & LOMB OPTICAL GO. 



552 St. Paul Street, Rochester, N. Y. 



New York 



Washington 



Chicago 



San Francisco 



Leading American Makers of Photographic Lenses, Microscopes, Projection Apparatiu 

 (Balopticons), Ophthalmic Lenses and Instruments, Photomicrographic Apparatus, 

 Range Finders and Gun Sights for Army and Navy, Searchlight Reflectors, 

 Stereo-Prism Binoculars, Magnifiers and other high-grade Optical Products 



that e^es may see ^ 



