PROCEEDINGS. 
525 
bian Exposition, at Chicago, in September, 1893. It will be 
published in the Journal of Geology, Chicago.] 
409th Meeting. November 11, 1893. 
President Goode in the chair. 
Thirty-eight members present. 
Mr. T. C. Mendenhall made a communication on The elec¬ 
trical congress of 1893 and its work in defining units. [Pub¬ 
lished in Science. 4°, New York, 1895, January 4, new series, 
vol. 1, no. 1, pp. 9-15.] 
Remarks were made by Messrs. Harkness, Mendenhall, Bige¬ 
low, and Wadsworth. 
Mr. H. A. Hazen read a paper on The mechanism of a tor¬ 
nado. [Published in the American Meteorological Journal. 8°, 
Boston, 1893, Nov., vol. 10, no. 7, pp. 301-304.] 
Remarks were made by Messrs. E. Farquhar, Paul, Eastman, 
Mendenhall, Abbe, and Hazen. 
410th Meeting. November 25, 1893. 
Vice-president Fletcher in the chair. 
Thirty-tw r o members present. 
Mr. F. L. 0. Wadsworth made a communication on The 
manufacture of very accurate straight-edges. [Published in 
Journal of the Franklin Institute. 8°, Philadelphia, 1894, July, 
vol. 138, no. 823, pp. 1-20. Republished in The American Ma¬ 
chinist, August 2, 1894.] 
It was discussed by Mr. Harkness. 
Mr. A. B. Johnson read a paper on The cruise of the Clover; 
further investigations into the aberration of audibility of fog 
signals. 
Remarks were made by Messrs. Hazen, Harkness, White, 
and Green. 
69—Bull Phil. Soc., Wash., Vol. 12. 
