specific Gravity, and comparative Wear of Gold. 141 
The upper frame, or that to which the upper pieces of coin 
are connected, is of brass, and consists of four bars, Fig. 1, AB, 
B b, ba, and aA, with three cross bars C c, C c, C c. 
The lower frame consists of a board, placed immediately 
under the upper frame, and is expressed in Fig. 2, by the letters 
LL. 
The upper frame is supported by two vertical boards, ex- 
tending the whole length of the sides B6 and A a, so that the 
ends of them are seen in Fig. 2, and are denoted by the letters 
DD, DD. These boards are fastened to the upper frame, and 
to the table upon which the apparatus stands, by hinges, so that 
the upper frame can move freely in the direction BA, but can 
have no motion in the direction perpendicular thereto. These 
vertical boards are omitted in Fig. 1; for, as the intention of this 
description is not to give a detail of all the parts of the instru- 
ments, but only to explain their manner of acting, I have taken 
the liberty to omit such parts as tended to produce an intricacy 
in the figures, without being necessary to this object. 
The disposition of the pieces of coin on the frames, is repre- 
sented in Fig, 1. N nn denote one of the connecting pieces, by 
which the upper pieces of coin are connected to the upper frame, 
and in which the small circle represents the position of the coin ; 
the large circle is the part which supports the weight, and nn 
the part by which it is connected to the upper frame. 
To avoid confusion, neither these connecting pieces nor the 
pieces of coin are represented in Fig. 2 ; but, instead thereof, a 
section of cne of these pieces is given in Fig. 3, upon a larger 
scale. 
In 1 his figure, LL is the lower frame, and C one of the bars 
of the upper frame ; y is one of the lower pieces of coin, which 
