608 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
he discussed the application of the laws of cooling of a sphere 
under various assumptions as to the initial distribution of tem¬ 
perature. 
Mr. C. H. Kummell made a communication on A Short, Rough 
Method of Computing the Probable Error. 
61st Meeting. April 30, 1890. 
The Chairman, Mr. Gore, presided. 
Present, ten members. 
Mr. G. W. Hill made a communication on The Secular Per¬ 
turbations of Two Planets Moving in the Same Plane, with Appli¬ 
cation to Jupiter and Saturn. 
62d Meeting. May 14, 1890. 
The Chairman, Mr. Gore, presided. 
Present, ten members. 
Mr. Marcus Baker made a communication on The Published 
Writings of Mr. E. B. Elliott, in which he presented a bibliog¬ 
raphy of Mr. Elliott’s publications, accompanied by remarks 
upon their scope and character. 
Mr. Artemas Martin made a communication on The Curve 
of Pursuit. 
Mr. J. F. Hayford made a communication on A Modification 
of the Ferrel Tide-Predicting Machine, which enables hourly 
readings of the tidal heights to be made in addition to the heights 
and times of high and low water, which latter the instrument 
has heretofore given. 
63d Meeting. January 7, 1891. 
The Chairman, Mr, Gore, presided. 
Present, ten members and guests. 
The first business transacted was the annual election of officers 
for the ensuing year. 
