r 



%^l 



W'l. Dire&kns fior fifing the common 'Mh 



■cr cinder ^ 'taken from a Paper in the late 



Dr. Bradley's 'Hdnd-'writmgi communi- 



cated i>y Nevil Ma/kelyne, /jJIronG?ner 



-iRojya/y ■ cmd< F. < R. S. 



%eadFfei).-i Qs m y|-rCROMETERS ? as Srft con- 

 JL'Vx tr i vec ^j being only adapted to the 

 'roeafuririg fmall angles, as the diameters of the Sufi 

 -and Moon, or otherplanets, and taking the diftance 

 -of fuch objects as appeared within the aperture of 

 the telefcppe at the lame time, were not of fo ge- 

 neral ufe as'thofe -which are contrived not only to 

 -anfwer the ends that the 'firft inventers aimed at s 

 but likewife, to take the difference of right afcen- 

 : iion and decimation of fuch obje&s as are farther 

 afunder than the telefcope will take in at once, but 

 : which pafs through the aperture of it at different 

 'times. Mr. Caffini firft made ufe of threads inter- 

 feeling one another at half right angles for deter- 

 mining the difference of right afcenfions and decli* 

 'nations of objects r>ear the fame parallel ; and this 

 apparatus being fimple and call ly procured is of 

 ^very great ufe to fuch as are not provided with a. mi- 

 crometer made according to the late improvements. 

 •But, where fuch a one is at hand, that method how- 

 ever curious Seed not -be made ufe of ? the micro- 



v metef 



