[ 46 ] 
VI. Directions for ufing the common Mi- 
crometer , taken from a Paper in the late 
Dr. Bradley’s Hand-writing ; communi- 
cated by Nevil Mafkelyne, Hfronomer 
Royal , and F. R. S. 
:-Read Feb. 20 , It >T I CROMETER S, as firft con- 
l 77 2 - trived, being only adapted to the 
umeafuring frnall angles, as the diameters of the Sun 
and Moon, or other planets, and taking the diffance 
<of fuch obje&s as appeared within the aperture of 
•the telefcope at the fame 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* 
but likewife, to take the difference of right afcen- 
fion and declination 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. •Caflini firff made ufe of threads inter- 
cepting one another at half right angles for deter- 
mining the difference of right afcenfions and decli- 
nations of obje&s near the fame parallel ; and this 
apparatus being fimple and eafily procured is of 
•very great ufe to fuch as are not provided with a mi- 
aerometer made according to the late improvements. 
.But, where fuch a one is at hand, that method how- 
ever curious need not be made ufe of, the micro- 
meter 
