*14 Mr. Sme Eton's Obfervathns on the 
-the primary point of o given, which would compleat eighty 
degrees'; I would then bife£t each of thole arches of i6°, as 
preicribed by Mr* Bird, and laying off one of them beyond 
the 8oth, would give the 8 8th degree : proceeding then by 
bifeflion, till I came to an arch of two degrees, laying that off 
from the Both degree, would give the point of ninety degrees. 
-Proceeding flill by bifeftion, till 1 had reduced the degrees into 
quarters = fifteen minutes each, I would there flop.; as from 
experience I know, that when divifions are over clofe, the ac- 
curacy of them, even by bife&ion, cannot be fo well attained as 
where they are moderately large. If a fpace of JL of an inch, 
which is a quarter of a degree, upon an eight-feet radius, is 
thought too large an interval to .draw the index over by the mi- 
crometer fcrew, this maybe fhortened by placing another line 
at the difiance of one-third of a divifion on each fide of the index 
line, in which cafe the fcrew will never have to move the index 
plate more than one-third of a divifion, or five minutes ; and 
the perfect equality of thofe fide lines from the index line may 
be obtained, and adjufted to five minutes precifely, by putting 
each of the fide lines upon a little plate, capable of adjuftment 
jo its true diftance from the middle one, by an adjufting 
fcrew. 
The above hint is not confined to the chord of lixteen degrees, 
.which prohibits the fubdivifions going lower than fifteen mi- 
nutes,: for . if it be required to have divifions equivalent to five 
.minutes upon the limb itfelf ; then I would compute the chord 
of 2i° 2o' only?, and laying it off four times from the primary 
point, the lafi: would mark out the divifion 85° 20 7 , pointed 
out by Mr. Bird ; fupplying the remainder to a quadrant, fi;om 
.the bifeded divifions as they arife, and not by the application of 
*other computed chords. 
u 
