428 Capt, Kater's improved Method of dividing 
in the mean time suffered any change of position, which may 
be known by the centre of the dot which is under B, being no 
longer found precisely under the intersection of its wires; and, 
should this have happened, the dot must be restored to its 
former position by moving the circle, previous to the final 
adjustment of the dot which is under the microscope A. The 
adjustable dots must thus be made successively to change 
places, till the line of reference arrives again in the field of the 
fixed microscope, when it is evident, if the intersections of the 
wires of the microscopes A and B are precisely distant seventy 
two degrees from each other, the line of reference will again be 
found accurately in the intersection of the cross wires of the 
fixed microscope, as it was at the commencement ; but should 
this not be the case, its distance from it will be equal to five 
times the error in the distance of the wires of the microscopes 
A and B, and this error is to be corrected by the micrometer 
of the microscope A,* and the whole operation repeated, always 
remembering to bring, in the first instance, the line of refer- 
ence accurately to the intersection of the wires of the fixed 
microscope, and carefully to repeat the various adjustments 
w'hich have been detailed. 
When, by repeated trials,the wires of the microscopes A and 
B are found to be at the required distance from each other, 
the divisions are to be cut on the limb of the instrument, the 
eye being assisted by viewing the cutting point through the 
fixed microscope. The first line, or zero, is to be made when 
* The line of reference may be brought to the intersection of the wires of the fixed 
microscope and the distance of the dot which is under A, from the intersection of its 
wires be measured by its micrometer screw, and this will be equal to five times the 
error in the distance of A and B. 
