80 LECTURES ON THE LUNAR THEORY. [LECT. XVII. 



and 



TT-dd) d'x . d?y 



- - 2n ' sin + + 2n' cos 



" dtj 



. Idx 

 > 



, T d<h \ dR . , dR 



or F + 2n' }= - - r sin <4 + -y cos A. 



\dt I ax ay 



doc cii/ 

 And from these, differentiating and substituting for -=- , -~ , we get 



fd(f> ,\ T7 f d^R 



(-J* + 2n = F -J-? COB 

 \o(< / |_ ax ' 



j~j ^- 



dxdy dy 



d"-R . , 



sin d> cos ' 



