V^ ESSAYS AND OBSERVATIONS 



rallax of the moon from the fun, every line 

 drawn on the difk will be expreffed by the fe- 

 conds of its correfpondent arch of the moon's 

 fphere. 



4. Let C be the center of the difk, W Ej 

 N S, the pr6jedl:ions oi w e the ecliptic, and 

 72 s 3. circle of latitude ; W N E being the up- 

 per or northern femicircle, and W S E the 

 lower or fouthern. Let V be the place of a- 

 ny given vertex on the difk, and v the cor- 

 refpondent point in the moon's fphere ; VA, 

 VB, perpendiculars to N S, WE, and v ay 

 •y 3 their correlatives. If the point v be the 

 true place of the moon, i. e. if the vifible pla- 

 ces of the fun and moon be the fame, then 

 will VA be the par. Ion. ^ ^ 0, and VB 

 the par. lat. to a fpedtator at the point V on 

 I the difk, or at the given vertex on the furface 

 of the earth. For the par. Ion. D ^} © is the 

 difference of the vif. Ion. D ^ obferved at 

 V and C : but the vif. long. D ^ obferved at 

 C, is the fame as if feen from A ; therefore 

 ^the par. Ion. B <7 is equal to the difference 

 of the vif. Ion. -^ /^ obferved at V and A, 

 which is equal to the arch v a the meafure 

 of V A. In like manner, V B may be proved 



to 



