( '5i ) 
the beginning of the Divifions (i. e. o°) it may be 
exa&ly parallel to that of the other ; this Speculum 
being turned towards the Obferver, and the other from 
him. PR is a Telefcope fix’d on one Side of the 
Odant, having its Axis parallel to that Side, and paf- 
fing near the middle of one of the Edges I K or I H of 
the Speculum I K G H j fo that half its Objed-Glafs 
may receive the Rays refleded from that Speculum, 
and the other half remain clear to receive them from 
a diftant Objed. The two Specula muflalfo be dif. 
pos’d in fuch manner, that a Ray of Light coming 
from a Point near the middle of the firft Speculum, 
may fall on the middle of the fecond in an Angle of 
70 Degrees or thereabouts, and be thence refleded in- 
to a Line parallel to the Axis of the Telefcope, and 
that a clear Paffage be left for the Rays coming from 
the Objed to the Speculum E F bv the Side H G. 
ST is a dark Glafs fix’d in a Frame, which turns on 
the Pin V by which Means it may be plac’d before 
the Speculum EF, when the Light of one of the Ob- 
jeds is too ftrong : Of thefe there may be feveral. 
Fig. III. In the diftind Bafe of the Telefcope, 
reprefented by the Circle abcdef . , are placed three 
Hairs, two of which, ac and b d, are at equal Dif. 
tances ftotn, and parallel to the Line gh, which 
paffes through the Axis, and is parallel to the Plane 
of the Oftant: The third f c is perpendicular to g h 
through the Axis. 
The Inftrumenr, as thus defcribed, will ferve to 
takeanyAngle not greater than 90 Degrees ; but if it be 
defign’d for Angles from 90 to 180 Degrees, the polifh’d 
Surface of the Speculum E F (Fig. z.)muft be turn’d 
towards 
