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. 



JULIEN'S POWER AND FOOT LATHES 



Use of Geologists, Mineralogists, Petrographers, Met- 

 allurgists, Mining Engineers, in SLICING and POL- 

 ISHING all hard substances, rocks, etc., and in prepa- 

 ration of MICROSCOPIC THIN SECTIONS. 



GUSTAVUS D. JULIEN 



3 Webster Terrace N EW ROCH ELLE, N. Y. 



PROVIDENT TEACHERS' AGENCY 

 120 Tremont Street BOSTON, MASS. 



We enroll and we recommend teachers and officers 

 for public and private schools, for normal and tech- 

 nical schools, and for colleges and universities. 

 Vacancies now for immediate service and for 1914- 

 15. Director, JAMES LEE LOVE, formerly of 

 Harvard Faculty. 



Bureau of Employment of the 

 Chemists' Club of New York, Inc. 



(Agency) 



52 East 41st Street, New York City. 



EMPLOYERS: We offer a list of 400 chemists and engineers 

 ranging from specialists to recent graduates, 

 either for industrial or analytical work, for 

 research or teaching. 



CHEMISTS: 



We desire the registration of all men wishing 

 to hear of vacancies in their special line. 



No charge to employers. 



Moderate fee to applicants. 



Prof. HERBERT R. MOODY, 

 Chairman, Club Committee. 



Jnst Published 



Third Mdition, Rewritten 

 Whipple — 



The Microscopy of Drinking Water 



By George C. Whipple, Gordon McKay Professor of Sanitary Engineering, 

 Harvard University. 



xxi+409 pages, 6 by 9, 73 figures and 6 plates in the text and 19 full-page 

 plates in colors. Cloth, $4.00 net. 



• This book serves as a guide to the water analysis and the water-works engineer, describing the 

 methods of microscopical examination, assisting in the identiiication of the common microscopic 

 organisms found in drinking water and interpreting the results in the light of environmental studies. 



It is also the purpose of this book to stimulate a greater interest in the study of microscopic 

 aquatic life and general limnology from the practical and economic standpoint. 



JOHN WIUrBV & SOJNS, Inc., 



432 Fourth Avenue, New York City 



London : 

 CHAPMAN & HALL, Limited 



Montreal, Can.: 

 RENOUF PUBLISHING CO. 



