SCIENCE-ADVERTISEMENTS 



Cramer's Precision Color=Filters 



FOR ALL PURPOSES 



Ibos and Visual 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. 



Our special booklets on " The Photography of Color Contrasts " 



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



Q. Cramer Dry Plate Company St. Louis, Mo. I 



Lantern Pictures 



of every sphere of ART, SCIENCE 

 and TECHNIC. artistically colored 

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Unger Sc Hoffmann, a.g. 



Dresden A. 77. GERMANY 



MARINE BIOLOGICAL LABORATORY 



WOODS HOLE, MASS. 

 ' biuiogrJcal Material 



1. Zoologry. Preserved mavcribl of all types of animali 

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2. Embryologry. Stages of some invertebrates, fishes (in- 

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3. Botany. Preserved material of Algae, Fungi, Liver- 

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QEORQB M. GRAY, Curator, Woods Hole, Mass. 



ELEVENTH EDITION 



THE MICROSCORE, 



an introduction to Microscopic Methods and to Histology, by 

 BraoN Henby Gage of (Dcrnell University. The 11th edition 

 has eight pages of new matter and corrections, otherwise it ig 

 like the 10th ed. Price $2.00 postpaid. 



COMSTOCK PUBLISHING CO., Ithaca, N. Y, 



WIUBV'S PUBLICATIONS 



ROBINSON— The Elements of Electricity. 



By Wirt Robinson, Lieutenant-Colonel, 

 United States Army, Professor of Chemistry, 

 etc., United States Military Academy, xiii 

 -f 596 pages, 6x9, 374 figures. Cloth, 12.50 

 net. 



TRA CY— NORTH— Descriptive Geometry. 



Part I — Lines and Planes. By John C. 

 Tract, C.E., Assistant Professor of Structural 

 Engineering, ShelBeld Scientific School of Yale 

 University. Part II — Solids. By Herbert 

 B. North, M.E., Assistant Professor of Draw- 

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 tific School of Yale University, and John C. 

 Tract, C.E. x-|-126 pages, 10^x7^ profusely 

 illustrated. Cloth, S2.00 net. 



Third Edition, Tboroagbly Revised 

 KERR — Power and Power Transmissions. 



By E.W. Kerr, Professor of Mechanical Engi- 

 neering, Louisiana State University, xii -|-391 

 pages, 6x9, 325 figures. Cloth, $2.00 net. 



MORECROFT— Continuous and Alternating 

 Current Machinery. An Elementary Text- 

 book for Use in Technical Schools. By J. H. 

 MoRECROFT, Assistant Professor of Electrical 

 Engineering, Columbia University, N. Y. ix 

 -f 466 pages, 5^x71, 288 figures. Cloth, $1.75 

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JOHN V/IUBV & SONS, Inc., 



432 Fourth Avenue, New York City 



London : 

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Montreal, Can.: 

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