Library, U. o. IN at. Museum. 



YOL. XLI. 



MAY, 1916. 



Established by BENJAMIN SILLIMAN in 1818. 



THE 



AMERICAN 



JOURNAL OF SCIENCE. 



Editor: EDWAED S. DANA. 



ASSOCIATE EDITORS 



Professors GEOKGE L. GOODALE, JOHN TEOWBRIDGE, 

 W. G. FARLOW and WI. M. DAVIS, of Cambridge, 



Professors ADDISON E. VERRILL, HORACE L. WELLS, 



LOUIS V. PIRSSON, HERBERT E. GREGORY 



and HORACE S. UHLER, of New Haven, 



Professor HENRY S. WILLIAMS, of Ithaca, 



Professor JOSEPH S. AMES, of Baltimore, 



Mr. -T. S. DILLER, of Washington. 



FOURTH SERIES 



VOL. XLI— [WHOLE NUMBER, OXCIJ. 

 No. 245— MAY, 1916. 



NEW HAVEN, CONNECTICUT. 



1916. 



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. Single numbers 50 cents. 



Entered as second-class matter at the Post Office at New Haven, Conn., under the Act 

 of March 3, 1879. 



