VOL. XL. JULY, 1915. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN- 



JOURNAL OF SCIENCE. 



Editor: EDWAED S. DANA. 



I 



ASSOCIATE EDITORS 



Professors GEOEGE L. GOODALE, JOHN TEOWBETDGE, 

 W. G. EAELOW and WM. M. DAVIS, of Cambridge, 



Professors ADDISON E. VEEEILL, HOEACE L. WELLS, 



LOUIS V. PIESSON, HEEBEET E. GEEGOEY 



and HOEACE S. UHLEE, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. J. S. DILLER, of Washington. 



FOURTH SE 



Rra 



llWffj 



VOL. XL— [WHOLE NUMJ3ER, CLXL1. 

 No. 235— JULY, 1915?" 



NEW HAVEN, CONNECTICUT. 



1915. 



THE TUTTLE-, MOREHOUSE & TAYLOR CO., PRINTERS, 123 TEMPLE STREET. 



Published monthly. Six dollars per year, in advance. $6.40 to countries in the 

 Postal Union ; $6.25 to Canada. Kemittances should be made either by money orders, 

 registered letters, or bank checks (preferably on New York banks). 



