﻿VOL. 
  XLIII, 
  MAY, 
  1917 
  

  

  Established 
  by 
  BENJAMIN 
  SIILIMAN 
  in 
  1818. 
  

  

  THE 
  

  

  AMERICAN 
  

  

  JOURNAL 
  OF 
  SCIENCE. 
  

  

  Editor: 
  EDWARD 
  S. 
  DANA. 
  

  

  ASSOCIATE 
  EDITORS 
  

  

  Professors 
  GEORGE 
  L. 
  GOODALE, 
  JOHN 
  TROWBRIDGE, 
  

   W. 
  G. 
  FARLOW 
  and 
  WM. 
  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 
  BALTiMeS^ 
  n 
  j 
  a 
  n 
  /* 
  

  

  Mr. 
  J. 
  S. 
  DILLER, 
  of 
  Washingt> 
  

  

  

  MAY 
  2 
  

  

  FOURTH 
  SERIES 
  <%tu 
  

   VOL. 
  XLIII- 
  [WHOLE 
  NUMBER, 
  CXCIII]. 
  

   No. 
  257— 
  MAY, 
  1917. 
  

  

  NEW 
  HAVEN, 
  CONNECTICUT. 
  

  

  1917. 
  

  

  THE 
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