vili SCIENCE.— ADVERTISEMENTS. 



Ives* Replicas of Rowland^s Gratings 



These replicas are made by a new process which gives gratings showing remark- 

 able definition in both the first and second order spectra. Even the smallest size shows in 

 direct sunlight all of the lines in Angstrom's map. The gratings are permanently- 

 mounted between tested glass plates and are no more subject to injury than glass prisms. 

 They all have approximately J 5050 lines to the inch. 



S. 111. IVES GRATINGS with ruled surface about 3-4x1 inch, fully utilizing the 



defining j)ower of spectroscopes of 1 inch aperture. Each . . • $6.00 



S. 112. IVES GRATINGS with ruled surfiice 1 3-8x1 7-8 Inches, fully utilizing the 



defining power of spectroscoiies of 1 1-4 inch aperture. Each . . $13. OO 



S. 113. IVES GRATINGS with ruled surface 1 3-8x1 7-8 Inches, specially selected. 



These specially sleeted gratings are almost absolutely equal in resolv- 

 ing power to an original grating of the same size, and will bear high 

 eyepiecing at full aperture in the second order spectrum. Each . $15.00 



THE SCIENTIFIC SHOP 



ALBERT B. PORTER 



SQENTIFIC INSTRUMENTS 322 Dearborn Street, CHICAGO 



JOHN WILEY & SOm ggS:^. 



A Treatise on Concrete, Plain and Reinforced. eases of the Mind and Nervous System iu the 

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 Taylor, M.E., Vice-President American Laboratory, Long Island City, N. Y. , some- 

 Society of Mechanical Engineers, and San- time Principal Assistant Chemist in the U. 

 FORD E. Thompson, S.B., Assoc. Mem. S. Department of Agriculture and Inspector 

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Elements of the Kinematics of a Point and the Road Materials. Am. Soc. for Testing Ma- 

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 O. James, Ph.D., Instructor in Mathematics Cloth, $3.00. 



and Astronomy, Washington University, St. Influence Lines for Bridge and Roof Computa- 



Louis. Small 8vo, xii + 176 pages, 39 fig- tions. By William H. Burr, C.E., Pro- 



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Descriptiv'e Geometry for Students of Engi- versity in the City of New York, and My- 



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A.M., Instructor in Descriptive Geometry in Engineering in Columbia University in the 



Harvard University. Second Edition. 8vo, City of New York 8vo, ix + 253 pages, 



viii + 198 pages, 128 figures. Cloth, $2.00. 158 figures (many full-page) and 3 folding 



Manual of Psychiatry. By J. Rogues de Fur- plates. Cloth, $2.50. 



sac, M.D., formerly Chief of Clinic at the Inorganic Chemistry. With the Elements of 

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 M.D. , Junior Assistant Physician, L. I. in the University of Nashville. Second edi- 

 State Hospital, Kings Park, N. Y. Edited tion revised. 8vo, viii + 651 pages, 76 fig- 

 by Joseph Collins, M.D., Profe.ssor of Dis- ures. Cloth, $3.00. 



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