SCIENCE 



New Series 



Vol. LIII, No. 1372 



Friday, April 15, 1921 



Single Copies, 15 Crs. 



NNUAL SUBSCKIPTION, $6.00 



BAUSCH & LOMB 



Biological 

 Colorimeter 



AN instrument constructed with the same accuracy character- 

 izing all of our Optical Measuring Instruments, at an 

 unusually low cost. 



Both tubes are adjustable, one by rack and pinion, and 

 have separate readings of scale. Readings are controlled by 

 observation only. 



The cups and cylinders which are re- 

 movable for easy cleaning, have parallel 

 glass bottom. 



The optical glass, of which the plun- 

 gers and prisms are made, is of high 

 transmission and freedom from color ; it is 

 ground, polished and mounted with the 

 greatest accuracy. 



Price — With tubes and scales 40 



mm long .... ^60.00 



Case extra 3-oo 



Bausch ^ Ipmb Optical @. 



409 ST. PAUL STREET ROCHESTER, N.M 



NEW YORK CHICAGO WASHINGTON SAN FRANCISCQI 



Makert 0/ Photographic Lenses, Microscopes, Projection Apparatus (Baloptlcons), Ophthalmic 

 Lenses and Instruments, Pholomicrographic Apparatus, Range Finders and Gun Sights /or Army and 

 Navy, Searchlight Reflectors, Stereo-Prism^ Binoculars, Magnifiers and other high-grade Optical 

 Products. 



LONDON 



