SCIENCE 



New Sebiss 



Vol. LHI, No. 13«1 



Friday, June 17, 1921 



Single Copies, IS Cts. 

 Annual Subsckiption, $4.00 



"Now, let me see" 



— you are delivering an informal talk, say, on your tra\ 

 are trying to recall an altitude or the height of a buildii ^. 

 most minds figures are vague, but clear, lasting impressicins-can 

 be made by actual pictures projected on a screen by 



^auscK"'[om 



BALOPTICON 



THE PERFECT STEREOPTICON 



This instrument projects opaque objects, including photographs, magazine il- 

 lustrations, post cards, maps, specimens, etc., as well as lantern slides. Even, 

 steady and safe illumination is assured by the new gas-filled Mazda lamp. For 

 clear pictures and easy operation specify the Balopticon. 



Bausch ^ Iptnb Optical Q. 



o-y 



New York 



552 St. Paul Street ROCHESTER, N. Y. 



Chicago Washington San Francisco London 



Leading American Makers of Photographic Lenses, Microscopes, Projection Apparatui 

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

 °inge Finders and Gun Sights for Army and Navy, Searchlight Reflectors, 

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



