[ x 7 2 ] 
the let fcrew, lb as to keep the objed interfered by 
-the wire; bat if fine fmooth fcrews, fuch as are ufed 
for micrometers to adronomical quadrants, are adapted 
to the indrument, as weli that commanding the ho- 
rizontal motion as the vertical, I apprehend, the 
management will be perfectly eafy and familiar to an 
obferver other wife weli pradifed. 
It is eafy to fee, that thofe ftars are to be preferred 
that are neared the heavenly body to be obferved ; 
and that, cater is paribus , thofe in fuch pofitions, as 
rife or fall flow, are bed: for determining their alti- 
tude ; and thofe that alter their azimuth flow, are bell 
for determining the azimuth. 
To avoid intricacy in defcription, I have fuppofed 
only two wires interfering each other at a right angle, 
in the focus of the telefcope : but, for the fake of get- 
ting a medium in fuch parts of the obfervations as 
depend on time, it will be proper to have, not only 
three perpendicular wires, parallel to each other as 
common, but alfo three horizontal wires ; the pro- 
portional didances of which being previoufiv deter- 
mined by obfervation, the oblique motions may (in 
parts not near the pole) be confidered as right 
-lines. 
This method is the more valuable as it is entirely 
free from the knowledge of refradions ; for fince the 
•computation gives the real altitude from the time 
given independent of refradions ; and fince the hea- 
venly body is equally affeded by refradion, at the fame 
altitude ; the computed altitude of the dar will give 
the real altitude of the heavenly body cleared of re- 
fradion, which never enters the quedion: and fince 
fuch dars may be chofen as will render the time in- 
tercepted 
