SCIENCE-ADVERTISEMENTS 



XI 



" THE CAMERA OF QUALITY " 



POLYGON CAMERAS 



with 



Rietzschel Double Anastigmats 



are the embodiment of all that is desirable in cameras. They are compact, small, and 

 light in weight, yet they are very reasonable in price: "They fit the Pocket." They 

 are made from miniature size up to 5x7 inches, in all styles. All are built of light but 

 indestructible metal ; all are leather covered ; all have leather bellows ; all have rising, 

 falling and cross front ; all have detachable lensboard ; all have quickly reversible 

 ground glass ; all are fitted with double anastigmats, the better ones with the finest 

 cemented lenses ever put on the market, in compound shutter. 



We also sell 



ERNEIVIANN Cameras and Double Anastigmats 

 MEVER CAMERA «& IINSTRUIVIEJNT CO., Inc. 



18 West 27th Street, NEW YORK 



rMPORTERS OF AND DEALERS IN SCIENTIFIC INSTRUMENTS 



DIONIC WATER TESTER 



Substitutes an extremely simple measurement of electrical con- 

 ductivity for the chemical reactions hitherto employed. Entire test 

 takes less than a minute to perform. By the use of this apparatus, 

 any unskilled person can detect and measure traces of impurities so 

 small as to escape chemical analysis. It has been found useful for 



measuring slight traces of im- 

 purities in distilled water, 

 sewage pollution in rivers, the 

 hardness of water, etc. "When 

 it is desired to know how much 

 of a known substance is pres- 

 ent in water, the Dionic 

 Tester gives the answer with 

 a rapidity and simplicity un- 

 approached by any other 

 method. 



Write for descriptive catalog to 



JAMES G. BIDDLE 



1211-13 ARCH ST. 



PHILADELPHIA, PA. 



When in Fbiladelpbia tx sure to visit our Permanent Exhibit of Scientific Instruments. 



