PHYSICAL AND LITERARY; ^H 



Art. V. 



An eajy Method of computing the Parallaxes 

 of the Moo?i ^ 3 hy . ' — . • 



TAB. IV. fig. I. 'I. If from 0, the 

 center of the fun, a right line ©W be 

 carried round, always touching the earth's fur- 

 face, this line will form a conical furfacej 

 which, being cut, by a plane paffing through 

 the center of the earth, at right angles to the 

 Une joining the centers of the fun and earth* 

 the fedtion, fo made, is the dijfk of the earth. 



2. The fame conical fur face will cut off a 

 circular portion of the moon's fphere, wn e s^ 

 within which, any arches, intercepted by 

 lines drawn from the center of the fun and ex- 

 tended to the difk of the earth, will be nearly 

 in the fame proportion to one another, as the 

 refpedive diftances intercepted on the difk. 



3. Hence, c being the center of the circular 

 poriion, ivce the ecliptic ; if the femidiameter 

 of the difk be expreffed by the number of fe- 

 conds in the a-rch c w or ce:=. horizontal pa- 

 rallax 



* November 6th, 1755. 



