510 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
Mr. Arthur Keith followed with a paper on The geology of 
Chilhowee mountain in Tennessee. [Published in this volume, 
pp. 71-88.] 
The paper was discussed by Messrs. Willis and Walcott. 
Mr. B. E. Fernow read a paper entitled Timber physics. [Not 
published. Its substance is contained in various reports and 
bulletins of the Division of Forestry, U. S. Department of Agri¬ 
culture.] 
This was discussed by Messrs. Harrington and Fernow. 
389th Meeting. May 7, 1892. 
President Gilbert in the chair. 
Thirty-one members and guests present. 
Mr. J. P. Iddings read a paper on The origin of igneous rocks. 
[Published in full in this volume, pp. 89-214.] 
This was discussed by Dr. Williams, of Baltimore, and Messrs. 
Cross, Clarke, and Lindgren. 
Mr. J. E. Watkins read a paper on John Stevens and his sons, 
early American engineers. [Published in a pamphlet entitled 
The Camden and Amboy Railroad ; origin and early history, by 
J. Elfreth Watkins, C. E., etc. 8°, Washington, press of W. F. 
Roberts (1892, published by the Pennsylvania R. R. Co.), pp. 
83-102.] 
390th Meeting. May 21, 1892. 
President Gilbert in the chair. 
Twenty-five members and guests present. 
Mr. H. A. Hazen read a paper on Scientific ballooning. [Pri¬ 
vately printed.] 
Remarks were made by Messrs. Woodward, Mendenhall, 
and Hazen. 
Mr. A. S. Christie read a paper on The method employed to 
find the latitude-variation tide. [Published in Bulletin of the 
