37 
new standards of weights and measures . 
Each knife edge was screwed to a thick plate of brass, the 
surfaces in contact having been previously ground together, 
and these plates were screwed to the beam, the knife edges 
being placed in the same plane, and as nearly equidistant and 
parallel to each other as could be done by construction. 
The support upon which the central knife edge rested 
throughout its whole length was formed of a plate of polished 
hard steel screwed to a block of cast iron. This block was 
passed through the opening before-mentioned in the centre 
of the beam and properly attached to a frame of cast iron. 
The stirrups to which the scales were hooked rested upon 
plates of polished steel to which they were attached, and the 
under surfaces of which were formed by careful grinding 
into cylindrical segments. These were in contact with the 
knife edges their whole length, and were known to be in 
their proper position by the correspondence of their extremi- 
ties with those of the knife edges. 
A well-imagined contrivance was applied by Mr. Bate for 
raising the beam when loaded, in order to prevent unneces- 
sary wear of the knife edge ; and for the purpose of adjusting 
the place of the centre of gravity, when the beam was loaded 
with the weight required to be determined, a screw carrying 
a moveable ball projected vertically from the middle of the 
beam. 
The performance of this balance fully equalled my expec- 
tations. With two hundred and fifty pounds in each scale, 
the addition of a single grain occasioned an immediate varia- 
tion in the index of one-twentieth of an inch, the radius being 
fifty inches. 
In using this beam, care should be taken that the ends of 
