SCIENCE 



Friday, August 3, 1900. 



Single Copies, 15 cts. 

 Annual Subsckiption, js.OO. 



WM. GAERTNER & CO. 



Astronomical and Physical Apparatus 



5347 AND 5349 LAKE AVE., CHICAGO 



SPECIALTIES 



Standard Apparatus of New and Improved Designs 

 Reading Microscopes and telescopes 

 Astronomical telescopes Heliostats 



Spectroscopes Dividing Engines, Comparators 



MiCHELSON Interferometers General Laboratory Apparatus 



bolometers UiMiversal Laboratory Supports 



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114 Fifth Avenue, New York. 



Company 



Book and Magazine Work in EngUsh and other 



languages, modern and ancieift. Hand or linotype com- 

 position. 



Technical Works : mathematical, physical, chemical, 

 crystallographic, mineralogic, biologic, and philologic. 

 Grammars and dictionaries ; interlinear, parallel and 

 phonetic texts. 



Examination Papers printed and delivered promptly in 

 sealed packages. Theses. Monographs. Catalogs. 



Translating, Transliterating, Editing. 



Samples anS estimates futnlsbO on application. 



MINERALS. 



Fine Apophyllite, Henlandite, Pectolite, Chabazite, 

 Datolite, Thaumasite Prehnite, from Paterson, N. J., at 

 from SOc. to $2.00. Pyrite Balls and Limonite Qeodes, 



from Sayerville, N. J., 20c. to 50c. each. Also a new stock of 



cut stones. Opals, Sapphire, Ruby, Zircon, Spessartite, Ruby Spinels, etc., at reasonable prices. 



WARD'S NATURAL SCIENCE ESTABLISHMENT, 30 to 40 College Ave., Rochester, N.Y. 



Willyeung 8" to I5"-110 Volt X-Ray Maehine. 



TAKE NOTICE 



AFTER VACATION comes the FALL WORK, you wiU need 

 Apparatus then. DON'T WAIT BUT PLACE YOUR ORDERS 

 NOW FOR FALL DELIVERY. You will get your goods in time, 

 SAVE MONEY, and enable us to arrange our summer work and hold our 

 trained force together. 



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WE MAKE A LARGE LINE OF SCIENTIFIC INSTRU- 

 MENTS OF PRECISION, MAINLY ELECTRICAL INCLUDING 

 GALVANOMETERS, STANDARDS OF RESISTANCE, PHO- 

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Repairs to all kinds of Instruments. Resistances readjusted in IN- 

 TERNATIONAL OHMS. 



CATALOGUE W-nS pages, free on application. 



I ELMER G. WILLYOUNG(LTphLll".^rA''), 82-84 Fulton St., New York | 



AUG 6 I900i 



