11 



SCIENCE-ADVERTISEMENTS 



Our Laboratory Spectrometers 



are sold in competition 

 with instruments of 

 European make to many 

 of the best laboratories 

 throughout the world. 



A New Student's 

 Spectrometer 



embodying several new features will be 

 ready for the market Sept. 1. 



Send for Catalog and further details. 



WM. GAERTNER & CO. 



Physical and Astronomical Instruments 



5345-49 Lake Ave. 



CHICAGO 



mp 



This air pnmp oper- 

 ates on an entirely new 

 and interesting princi- 

 ple. No mercury is 

 osed. With a fore-vac- 

 uum of .01 mm. it will 

 evacuate a 6-liter vessel 

 from 10 mm. to .00001 

 mm. in 3 minutes. It 

 pumps vapors as well 

 as gases, greatly sim- 

 plifying the process of 

 evacuation. 

 Gaede Molecular Air Pump with 110 V Motor and t-iegulator 



Write for Illustrated Descriptive Price List No. 6 



The Gaede Molecular Air Pump Is imported into the United States by 



JAMES G. BIDDLE 



1211-13 ARCH ST. Special Representative PH I LADELPH I A, PA. 



When in Philadelphia be sure to visit our Permanent Exhibit of scleBtiflc apparatus 



