SCIENCE-ADVERTISEMENTS 



Cramer's Precision Color=Filters 



FOR ALL PURPOSES 



Ibo8 and Visnal Luminosity for landscape, portrait and telephoto work. 



Tricolor Filters for 3-color work. Contrast Filters for special color work. 



Micro-filters for Photomicrography and Spectroscopy. 



Oar special booklets on " The Photography of Color Contrasts " 



and "Trichromatic Work" free to interested parties on request. 



G. Cramer Dry Plate Company 



St. Louis, Mo. 



WM. GAERTNER & CO. 



Astronomical and 

 Physical Apparatus 



SPECIALTIES 



Standard Apparatus of New and Improved Designs 

 Readins Microscopes and Telescopes 



DiTtdins Engines 



Comparators 



General Laboratory Apparatus 



Universal Laboratory Supports 



Astronomical Telescopes 



Spectroscopes 



Michelson interferometers 



Heliostats 



5345 and 5349 Lake Ave. 



CHICAGO 



Portablo Equatorial Telescope with 

 Driving Clock. 



KENT— Inyestigating an Industry. A Scientific PICKELS and TF/LE 7— Text-Book on Railroad 



Diagnosis of the Diseases of Management. By 

 William Kent, Consulting Engineer. With 

 an Introduction by Henry L. Gantt, Author 

 of " Worli, Wages and Profit. ' ' 12mo, xi + 126 

 Cloth, Sl.OO net. 



Surveying. By W. G. Pickels, Instructor in 

 CivU Engineering, University of Illinois, and 

 C. C. Wiley, Instructor in CivU Engineering, 

 University of Illinois. 16mo, ix+263 pages, 

 99 figures. Morocco, S2.50 net. 



DYSON — Screw Propellers and Estimation of 

 Power for Propulsion of Ships. By Captain 

 Chablbs W. Dyson, U. S. Navy. Vol. I., 

 Text, 8vo, v + 142 pages, 24 figures. Vol. II., 

 Atlas. Portfolio size, consisting of 32 double 

 page charts. Both volumes. Cloth, S7.50 net. 



MORITZ—V\ane and Spherical Trigonometry. 



(With five-place Tables.) A Text-book for 

 Technical Schools and Colleges. By Robert 

 E. MoRiTZ, Ph. D., Ph.N. D., Professor of 

 Mathematics in the University of Washington. 

 8vo, xvi -1-453 pages, 224 figures. Cloth, S2.60 

 net. 



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SCIENTIFIC PUBLICATIONS 



432 Fourth Avenue, New York City 



London : 

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Montreal, Can.: 

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