44 Afr. Smeaton*s Ohfervaiions on the 
from the point in the tangent, and there hold it fteadily faft $ 
the tangent point being placed upon the fixed block before- 
mentioned* 
Ufe of the dividing Plate in the Graduation of Infruments . 
Our dividing plate is now ready for the reception of an 
inftrument; fuppofe it a quadrant, whofe radius, however, 
muft not exceed the radius of the dividing plate : It is to be 
laid upon the face of the dividing plate, and a weight, or 
weights, equivalent to that of the quadrant, is placed on the 
oppofite fide, to balance it. It muft alfo be fuppofed, that the 
quadrant is made with a view to be divided by this engine; and 
consequently, that the central cylinder is fo well adapted, and 
nicely fitted to the center hole of the quadrant, that the center 
cylinder can be removed, in order for the limb to be divided, and 
again replaced, without fenfibly altering its center. This being 
the cafe, let a piece of metal be turned, to apply to the quadrant, 
perfectly like its center cylinder at the upper end, and turned 
nicely to fit the central hole in the dividing plate, at the lower 
end ; then, the quadrant being fixed with proper fattening 
fcrews, I would cut the divifions with a beam compafs ; and, if 
a fixed point is affumed, viz. the center of the tangent point 
for the index ; then the beam compafs being always opened to 
the computed length of the tangent of the circle of divifions, it 
will be fufficiently near for cutting the divifions, fquare to the 
circular arches between which they are placed. 
It will alfo be proper (to prevent unequal expanfions) that the 
beam of the compafs ftiould be formed of a piece of clean- 
grained white fir*, and that the length between the points be 
inclofed in a tube of tin or brafs ; without touching the beam, 
except 
