330 Prof. H. Hennessy on the Precession calculated 



most probable % that is instead of -™ or even smaller 



fractions hitherto accepted, I find that P x becomes 56"*05. 

 By Pratt's formula and the numerical values he employs, 

 except for E, I find 



P 1 = 54 // -879. 



If we take ^n f° r the Moon's mass in Poisson's formula, y 



becomes 2*2062, and 



P 1 = 53"-574. 



If we change 7 to 80 in Pratt's formula with 



The value for the observed precession now generally ad- 

 mitted is 50 //# 37. It is therefore manifest that the difference 

 between this and the precession of a homogeneous equi- 

 elliptic spheroid cannot be admitted to be as great as 

 Mr, Hopkins has declared it to be. From the values of P x 

 which I have calculated we should have 



P 1 -P = 5"-68and4 // *507, 

 with the Moon's mass =-wk\ 



Pi-P=J"Jj7,and 2"-58, 



if we take the Moon's mass = q~. 



On calculating P with the Moon's mass = ^, Sun's mass 



354936, 7 is 2*25395. If we take for I its value in 1852, or 

 23° 27' 32", and make 



m=359°-9931, - = '0027303, E= *_ 

 ' n 293*46' 



the following calculations can be made : — 



* See Colonel Clarke's paper in the Philosophical Magazine for August 

 1878, where he maintains that recent geodesical results tend to increase 

 the value of the Earth's ellipticity and to make the measured value 

 approach to that obtained from pendulum observations. 



