C ”9 3 
Diameter of aperture of objed-glafs 
Height of glafles 
Height of iilvered part of index-glafs 
Height of unfilvered part of ditto 
Height of filvered part of horizon-glafles 
Height of unfilvered part of ditto 
Part 
s of ai 
1 Inch 
> 3 ° 
0,40 
0,50 
> 9 ° 
1,37 
’ 5 ° 
0,63 
°>77 
,40 
0,50 
0,60 
>25 
°\33 
0;42 
> 6 5 
0,80 
0>95 
If the telefcope has a common objed-glafs, the 
firft aperture of _%.ths of an inch will be moft con- 
venient ; but if it has an achromatic objed-glafs, one 
of the other apertures of -j—ths or ^L-thsof an inch, 
will be moft proper. The field of view of the 
telefcope fhould be 5 or 6 degrees, and the objeds 
fhould be rendered as diftind as poflible throughout 
the whole field, by applying two eye-glafles to the 
telefcope. The breadth of the glafles fhould be de- 
termined as ufual, according to the obliquity with 
which the rays fall on them and the aperture of thy 
objed-glafs. 
I fhall conclude this paper with fome eafy rules 
for finding the apparent angular diftance between 
any two near land objeds by the Hadley’s qua- 
drant. 
To find the angular diftance between two near 
objeds by the fore-obfervation. Adjuft the fore- 
horizon-glafs by the objed intended to be taken as 
the dired objed ; and the angle meafured by the 
fore-obfervation on the arch of the quadrant between 
this objed and any other o^ed feen by refledion will 
be the true angle between them as feen from the 
centre of the index^glafs. But, if the quadrant be 
already 
