C 221 3 
XIII. On an Improvement in the Manner of dividing astronomical 
Instruments . By Henry Cavendish, Esq. F. R. S. 
he great inconvenience and difficulty in the common 
divisions by putting the point of the compass into them, and 
from the difficulty of placing that point mid-way, between two 
scratches very near together, without its slipping towards one 
of them, and it is this imperfection in the common process, 
which appears to have deterred Mr. Troughton from using 
it, and thereby gave rise to the ingenious method of dividing 
described in the preceding part of this volume. This induced 
me to consider, whether the abovementioned inconvenience 
might not be removed, by using a beam compass with only 
one point, and a microscope instead of the other ; and I find, 
that in the following manner of proceeding, we have no need 
of ever setting the point of the compass into a division, and 
consequently that the great objection to the old method of 
dividing is entirely removed. 
In this method, it is necessary to have a convenient support 
for the beam compass : and the following seems to me to be 
as convenient as any. Let C C C ( Fig. 1. ) be the circle to be 
divided, B B B a frame resting steadily on its face, and made to 
slide round on it with an adjusting motion to bring it to any 
required point : d $ is the beam compass, having a point near 
MDCCCIX. G g 
Read May 18, 1809. 
method of dividing, arises from the danger of bruising the 
