PHYSICAL ASTRONOMY. 



of the investigation, supposing that it was the 

 quantity of motion (not of momentum] that must be 

 equal in the meniscus and in the entire spheroid. 

 D'ALEMBERT was the first who corrected this 

 mistake. 



When the angular motion is computed, t being the 

 time of the diurnal, T of the annual revolution of 

 the Earth, c the compression at the poles, and a 

 the radius of the equator, 2 the declination of the 



Sun ; it is found that - = =- X - sin 2 cos 3 . 

 v T* a 



This is the same with SIMPSON'S Theorem, Miscel- 

 laneous Tracts, London, 1757, Prob. 2. p. 14. 



Next, supposing t and 2 to vary, so as to get the 

 fluxion of the precession, and afterwards integra- 

 ting, the precession for an entire year is found 



= 360 X ~ X cos Obi. SIMPSON, ibid. p. 17. 



From this, SIMPSON computes the precession arising 

 from the Sun's action, supposing the Earth to be a 



homogeneous spheroid, and its compression - 



ZiO 1 



to be 2 I'M. Professor ROBERTSON of Oxford 

 makes the precession 21 ".03. Phil. Trans. 1807. 

 p. 82. FRISIUS makes it 2 1".J. on the same hypothe- 

 sis. TheoriaDiurni Motus : Opera, torn. m. p. 288. 



if 



