C i 5*-y 
towards the Obferver ; the fecond IKG H muft be 
brought forward to thePofition N Ofo as to receive on 
its Middle the Rays of Light from the middle of the firft 
in an Angle of about 15 Degrees, their Surfaces being 
perpendicular to one another when the Index is brought 
to the End of the divided Arch next C ; and this fecond 
mull: hand five or fix Inches wide of the firft, that 
the Head of the Obferver may not intercept the Rays 
in their Pailage towards it, when the Angle to be ob- 
ferv’dis near 180 0 . The fmaller Speculum is fix’d 
perpendicularly on a round brafs Plate, tooth’d on the 
Edge ^ and may be adjufted by an endlefs Screw. 
In order to make an Obfervation, the Axis of the Te- 
lefcope is to be direded towards one of the Objefts, the 
Plane of the Inftrument palfing as near as may be 
through the other, which rauft lie to that Hand of 
the Obferver, as the particular Form of the Inftru- 
ment may require ; viz. the fame Way that the Spe- 
culum E F does from 1KGH, if it be compofed ac- 
cording to this Figure and Befcription. The Obfer- 
ver’s Eye being applied to the Telefcope, fo as to keep 
fight of the firft Object \ the Index muft be moved 
backward and forward till the fecond Objeft is like- 
wife brought to appear through the Telefcope, about 
the fame Diftance from the Hair ef (Fig. 3.) as the 
firft : If then the Objects appear wide of one another, 
as at i and k, the Inftrument muft be turn’d a little 
on the Axis of the Telefcope, till they come even, 
or very nearly fo, and the Index muft be remov’d till 
they unite in one, or appear clofe to one another in a 
Line parallel to cf, both of them being kept as near 
the Line g h as they can. If the Inftrument be then 
turn’d 
