PHILOSOPHICAL SOCIETY OF WASHINGTON. 
534 
416th Meeting. February 17, 1894. 
President Fletcher in the chair. 
Thirty-nine members and guests present. 
Announcement was made of the election to membership of 
John Thompson Hedrick. 
Mr. G. K. Gilbert made a communication on A proposed 
machine for the computation of least square problems. [Not 
published.] 
It was discussed by Messrs. Abbe, Harrington, Baker, Bige¬ 
low, and Gilbert. 
Mr. F. W. Clarke made a communication on The atomic 
weight of oxygen; a study in constant error. 
This was discussed by Messrs. Kummell, Abbe, Doolittle, 
Farqupiar, and Clarice. 
417th Meeting. March 3, 1894. 
President Fletcher in the chair. 
Thirty-nine members present. 
The Secretary read a letter from the Geographical Society of 
the Pacific inviting the Philosophical Society of Washington to 
be represented by one or more delegates at a Conference of Geog¬ 
raphers to be held at the California Midwinter International 
Exposition, May 4, 1894. 
Mr. George Davidson read a paper on A method of determin¬ 
ing the periodic error of a micrometer screw. [Published in 
U. S. Coast and Geodetic Survey Report for 1892. 8°, Washing¬ 
ton, 1893, Appendix 9, pp. 505-513; also separately.] 
This was discussed by Messrs. Paul, Baker, Wadsworth, 
Bigelow, and Davidson. 
Mr. C. F. Marvin read a paper upon An automatic mercurial 
barograph, which was exhibited. [Not published. For descrip¬ 
tion of instrument see pamphlet published by the Weather 
