486 

 Also 



Thus we get 



or 



Mr. J. Prescott on. the 



■=rg- = </, the acceleration due to gravity at 

 the earth's surface. 



p 4 tt 3B 



2 

 B 



RV, 



r 9 _±TT ' 



e Ra> 2 3 5 , R 5 a> 2 ~2' 



(«) 



If /9 is constant then e may be considered constant and 

 B=/oeR 5 . Then our equation would give 





9 3 g 1 

 € Rw 2 5 6 Kco 2 "~2 



But 



i& = 289 - 



Hence 



i=231. 



e 



It is certain, however, that e is not constant. We cannot 

 find e therefore without knowing the value of the coefficient 



B. Now this coefficient is given in terms of j p/3 4 dft, a 



Jo 

 quantity which does not contain e, by the theory of the 

 precession of the earth's axis. By assuming a reasonable 

 law for p we can then find B, and thence determine e. 



Fig. 2. 



A. 2¥ 



The potential of the earth at an external point P (Hg. 2) is 



V = fK7r(~-^(3cos 2 0-l)). 

 6 {.r Or ' J 



The force exerted by the earth perpendicular to OP on 



