Astronomical Circles and other Instruments. 
45 1 
division with the cutting point, and proceed in this manner 
round the whole circle, remembering that when a division is 
in the intersection of the wires of A, another division should 
be found precisely in that of B, and this affords a very severe 
test of the accuracy of the work as it proceeds. 
Having thus obtained divisions of twenty-four degrees, tliese 
are again to be trisected precisely in the same manner, and 
with all the precautions before detailed, placing, should it be 
necessary, the microscope B, at the distance of two divisions, 
or forty-eight degrees, from the fixed microscope, and trans- 
ferring the adjustable dots through two divisions instead of one, 
which will bring the new divisions under the microscope A, 
when the adjustable dots may be taken off. 
The circle is now divided into portions oi eight degrees each, 
and these are to be continually bisected, till we arrive at divi- 
sions of half a degree; but as it is presumed that the centres of 
the microscopes A and B, cannot be brought nearer to each 
other than eight degrees, it becomes necessary to lake distant 
divisions, and to bisect twenty-four degrees. For this purpose, 
having brought the line of reference to the intersection of the 
wires of the fixed microscope, and verified the adjustment of 
the cutting point, place the microscope A, as near to the fixed 
microscope as convenient, with the intersection of its cross 
wires half way by estimation between any two divisions, and 
at the distance of twelve degrees place the microscope B, 
causing the angles of its cross wires, by means of the micro- 
meter screw, to be bisected by the division under it. Fix an 
adjustable dot beneath the intersection of the wires of A, and 
see that it passes through that of B, as formerly directed. 
Adjust for distinct vision, in the manner which has already 
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