426 Capt, Kater's improved Method of dividing 
whether the line of reference appears to change its position. 
If it is perfectly stationary in every situation of the eye, the 
adjustment of the microscope is correct; if not, the remaining 
parallax must be destroyed by moving the object glass, which 
must afterwards be secured by means of its nut. 
The next step is to adjust the cutting frame. To this end, 
place the projecting pieces a, a, of the cutting frame on the 
face of the limb of the instrument, when the dot will be at a 
proper distance from the microscope for distinct vision. Slide 
it through the field of view, and examine whether its centre 
passes accurately through the intersection of the cross wires, 
and if not, cause it to do so by means of the screws F and F.* 
This adjustment should be most carefully examined in every 
part of the process of dividing, as it is essentially necessary to 
the accuracy of the operation. 
Place the microscope A, as near to the fixed microscope as 
conveniently may be (leaving, however, sufficient space to 
use the cutting point), and clamp it firmly to the arc. Fix 
the microscope B at the distance of seventy-two degrees by 
estimation from and bring the intersections of their wires 
between the circles which are to limit the divisions. Place an 
adjustable dot under A, with its centre precisely in the inter- 
section of the cross wires. Unclamp the circle, and turn it on 
its axis till the adjustable dot arrives at the intersection of the 
cross wires of B ; and should the centre of the dot not pass 
* The same thing might, perhaps, be as conveniently efFected by giving a motion 
to the cross wires of the fixed microscope, and fine lines intersecting each other at 
right angles may be used instead of the dot (as in the adjustable pieces) should it be 
thought preferable. 
f This may be readily done by means of the figures usually engraved on the limb 
previous to the operation of dividing. 
