PROCEEDINGS. 
489 
formula. [For an abstract see Science, 1899, May 12, new series, 
vol. ix, no. 228, p. 686.] 
Discussed by Messrs. Farquhar, Martin, and Gore. 
Mr. Gore exhibited a number of lantern slides illustrating 
geodetic work in Spitzbergen. 
502d Meeting. May 13. 1899, 
President Tittmann in the chair. 
Twenty-two members and guests present. 
Informal communications were made by Mr. Wead on Color 
effect in stereoscopic pictures, by Mr. Baker on A certain 
rhythmic problem, by Mr. Tittmann on The results of tidal ob¬ 
servations at the mouth of the Elbe, and by Mr. Gore on Some 
Spanish geodetic literature. 
Mr. Gore read a paper on Geodetic work in Spitzbergen. 
Discussed by Mr. Preston and the author. 
Mr. See read a paper entitled An extension of Helmholtz’s 
theory of the sun to the case of a heterogeneous sphere made up 
of gaseous layers of uniform density. 
Discussed by Messrs. Bauer, Wead, Littlehales, Hayford, 
and the author. 
503a Meeting. May 21 , 189§. 
Vice-President Sternberg in the chair. 
Twenty-nine members and guests present. 
Mr. Radelfinger read a paper entitled Recent progress in the 
theory of linear differential equations. [Published in the Bulletin 
of the Philosophical Society of Washington, vol. xiv, pp. 21-35 ; 
also an abstract in Science, 1899, June 16, new series, vol. ix, no. 
233, p. 849.] 
Discussed by Messrs. Littlehales and Gore. 
