to ascertain a Standard of Weight and Measure. 143 
(§.11.) It was necessary to measure the exact size, and cor- 
rectness of figure, of this sphere. For this purpose was made a 
woodengauge or frame abcde,["T?ibN. fig. 2.) in which the sphere 
was placed, upon semicircular pieces within, lined with green 
cloth to prevent bruising it : upon this frame was placed a brass 
square klmn , whose sides were about T ~- inch in length more 
than the diameter of the sphere. This square, by raising or 
lowering the screws or s, was easily made to coincide with a 
plane passing through the centre of the sphere, p is a micro- 
meter screw, the interior extremity of which is brought just to 
touch the surface of the sphere, while the opposite side bears 
gently against the interior side of the frame at 0 ; and, by turn- 
ing the sphere round, so as to present different diameters to 
these points of contact, any variety in the diameter may be 
seen by the index /, and plate q, divided into io,oooths inch. 
To render this operation more convenient, three great circles 
were drawn with a pencil upon the sphere, at go 0 distance from 
each other, (the two former were traced by the artist in the 
lathe, while the sphere was making, and the third was drawn 
from them, ) and each was divided into 8 equal parts. The im- 
mediate result of these experiments would only give the diffe- 
rences, and not the absolute quantity, of the diameter ; for this 
purpose, a brass ruler r, fig. 3. was made, of such a length 
as just to go within the brass frame klmn ; and, being sub- 
stituted in the place of the sphere, could easily be compared 
with any given diameter, and afterwards measured with the 
divided scale, fig. 1. With these instruments I made the fol- 
lowing observations, August 31, 17 g 6 , the thermometer being 
at 
