CONSTRUCTION OF A NEW ELECTRICAL BALANCE. 
425 
these last are cemented below into a neat brass ferule, /, so as to be easily inserted 
when in use into a spring- socket, y, fig-. 7, attached to a narrow plate of brass or 
wood y y'. This plate is temporarily fixed in the base of the cag-e, as at s, fig. 3, in a 
line perpendicular to the direction of the needle when at rest. A portion of the 
interior of the plate is removed, as at y y', and a screw, s, figs. 7 and 3, terminating 
in a milled head passed through it into a nut fixed in the wood underneath ; the whole 
may be thus accurately adjusted so as to bring the proof plate q just in contact with 
the disc of the needle, when the index v v is at zero. 
Either of the discs above mentioned may be connected with an insulated charged 
body, S, fig. 9, through a round hole H drilled in one of the glass sides of the cage : 
this hole is about *6 of an inch in diameter, and is placed so as to admit of the exter- 
nal body being connected with the back of the disc ; the communication is effected 
through the intervention of a light wire, which we may suppose to join p S, figs. 3 
and 9. The wire is supported horizontally in a neat ball of wood attached to the ex- 
tremity of a vertical rod of glass, placed in the base of the cage in the way already 
described ( v .), fig. 7- 
One of the extremities of the connecting wire terminates in a fine point to be 
inserted in the back of the fixed disc y opposed to the disc of the needle ; and the 
other extremity either in a small knob or a point, as the circumstances of the ex- 
periment require. 
f. The brass circle A t I turns freely about its centre under a light transverse piece 
of brass, B B', about 4 inches in width at its extremities, and -3 of an inch in thick- 
ness : this piece is fixed on short vertical pillars i i', &c., so as to be raised above the 
roof of the cage, the whole being secured by screws and nuts. 
o. The transverse piece B B' is accurately centered, and a circular opening drilled 
through the centre at x of about an inch or more in diameter ; for the sake of light- 
ness it is formed as represented in the figure. Immediately in the centre of this 
piece there is united to it a short plate of brass, D, fig. 15, three inches in diameter 
and three tenths of an inch thick. This plate has a drawn brass tube, P, of an inch 
bore, fixed underneath it, which, passing centrally through the frame B B', retains the 
circle A t I, figs. 3 and 14, in its place beneath. There is a similar plate and de- 
scending tube, x, figs. 3 and 15, placed immediately over this, carrying the frame ax a' 
for the suspension threads of the needle. The hollow tubes fit closely one within the 
other, as indicated in fig. 15 ; and the faces of contact of the two plates are ground 
fair together, so as to admit of the upper plate being turned upon the lower one with- 
out materially deranging its vertical position. 
r. In order to estimate the angular quantity which the upper plate has been turned, 
there is a graduated circle, i f, figs. 3 and 15, of six inches in diameter, sustained 
without the edge of the fixed plate D by light arms projecting from an interior ring. 
This ring is accurately fitted to the circular edge of the fixed plate within, so as to 
admit of its turning upon it as a centre for a short distance, with some friction ; by 
3 i 
MDCCCXXXVI. 
