136 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
appointed by the Chair. After some diScussion by Messrs. 
HARKNEss and ELuiorT it was so ordered, with the additional 
provision that this appointment be made for each paper separately. 
Mr. G. W. Hitt made a communication on 
PLANETARY PERTURBATIONS OF THE MOON, 
which was yet unfinished when he yielded the floor to Mr. G. K. 
GILBERT, who made a communication on 
GRAPHIC TABLES FOR COMPUTING ALTITUDES FROM BAROMETRIC 
DATA. 
This paper will appear in the Bulletins of the U. S. Geological 
Survey. 
6TH MEETING. JUNE 6, 1883. 
The Chairman presided. 
Present, sixteen members and guests. 
Mr. G. W. Hit concluded his paper on 
CERTAIN POSSIBLE ABBREVIATIONS IN THE COMPUTATION OF THE 
LONG-PERIOD PERTURBATIONS OF THE MOON’S MOTION 
DUE TO THE DIRECT ACTION OF THE PLANETS. 
[ Abstract. ] 
Hansen has characterized the calculation of these inequalities as 
extremely difficult. However, it seems to me that if the shortest 
methods are followed there is no ground for such an assertion. The 
work may be divided into two portions independent of each other. 
In one the object is to develop, in periodic series, certain functions 
of the moon’s coordinates, which in number do not exceed five. 
This portion is the same whatever planet may be considered to act, 
and hence may be done once for all. In the other portion we seek 
the coefficients of certain terms in the periodic development of 
certain functions, five also in number, which involve the codrdinates 
of the earth and planet only. And this part ofthe work is very 
similar to that in which the perturbations of the earth by the 
planet in question are the things sought. And as the multiples of 
the mean motions of these two bodies, which enter into the expres- 
