JUN 3 



1905 



SCIENCE 



New Series. ,-(-1 -> \-v "TrTjiT-^A v Tttmt? 9 1 Qfil^ Single Copies, 15 Cts. 



Vol. XXI. No. 544. Vo ^ \ ^ TKIDAY, JUiNii Z;, ^.V^O. ANNUAL SUBSCRIPTION, $5.00. 



Physical and Electrical Measuring Apparatus 



My long-standing connection with the leading foreign instrument makers enables me to import appa- 

 ratus at the most favorable "duty free" rates, while my facilities for the placing of domestic orders are 

 unecjualed. Hence lam in a position to care for the entire list of apparatus which you may wish to pur- 

 chase and can quote you a lump figure which can not be underbid. Try the experiment and see if this is 

 so; get my prices on your entire list. 



Write for pamphlet 575 — "Catalogues of Interest to Scientific Men." It will prove a genuine aid in 

 keeping your file up-to-date. 



JAMES G. BIDDLE, 1114 Chestnut Street, Philadelphia 



Special Agent for : Weston Electrical Instrument Co., Electric Storage Battery Co., Hartmann & Braun, Cambridge 

 Scientific Instrument Co., Siemens & Halske, Max Kohl, Otto Wolff. Society Genevoise, William Gaertner >.t Co., Carl 

 Zeiss, Emil Gundelach, A. T. Thompson & Co., ValderBros,, R. W. Paul, etc. 



Q^QJ^ jyj^'^jg^ For Field Work there is nothing as convenient as 



_ the Penfield Contact Goniometer, light, exact, dura- 



ble, inexpensive. We are the only firm that handles these celebrated instruments. 

 Send for special circular describing Models A. and B. and the combined Ai-m Protractor 

 and Goniometer. 50c each, postage 2c extra. 



WARD'S NATURAL SCIENCE ESTABLISHMENT (Mineral Department), Rochester, N. Y. 



Ives* Replicas of RowIand^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 



tlefliiing power of spectroscopes of 1 i!>ch aperture. Each . . . $(>.00 



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



defining power of spectroscopes of 1 1-4 inch aperture. Each . . $12,00 



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



These specially selected gratings are almost absolutely equal in resolv- 

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

 eyepiecing at full aperture in the second order spectrum. Each . $15 OO 



THE SCIENTIFIC SHOP 



ALBERT B. PORTER 



SCIENTIFIC INSTRUMENTS 322 Dearborn Street, CHICAGO 



