JUL 1 



SCIENCE 



New Series. vIT' TTd-r, a v Tttmt? "^H 1 QflP^ Single Copies, 15 Cts. 



Vol. XXI. No. 548. oV) 5^ TKliJAY, J UJNJj. 0\J, IvyJO. Annual Subscription, 85.00. 



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 tSOSO lines to the inch. 



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



clefining power of spectroscox>es of 1 inch aperture. Each . . . $6.00 



S. 112. IVES GRATINGS Avith 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 Avith 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 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 



A TIMELT BOOK OF UNQUESTIONED AUTHORITT 



in which the results of the patient, minute observations 

 made through many years by the leading engineers of 

 the world are stated lucidly and with the least possible 

 technicality, so that any one interested may understand the 



Problems of the Panama Canal 



Including the Physics and Hydraulics of the River Chagres, the Clima- 

 tology of the Isthmus, and the Cut at the Culebra. By BRIG.-GEN. 

 HENRY L. ABBOT (U. S. Army, Retired), Late Colonel Corps of 

 Engineers, Late Member of the International Comite Technique, and Con- 

 sulting Engineer of the New Panama Canal Company. $1.50 net (postage 12e.) 



THE MACMILLAN COMPANY, Publishers, 64-66 Fifth Ave., New York 



