new Eledlrical Jnjlrumcnt. 257 
ele&rometer is annexed to each. The letters of reference indi- 
cate the fame parts in both figures. 
ABCD is a flat tin plate, thirteen inches long and eight 
inches broad ; to the two Ihorter Tides of which are foldered 
two tin tubes AD and BC, which are open at both ends. DE 
and CF are two glals flicks covered with healing wax by means 
of heat, and not by diflolving the fealing wax in ipirits. They 
are cemented into the ‘lower apertures of the tin tubes, and 
alfo in the wooden bottom of the frame or machine at E and 
F, fo that the tin plate ABCD is fupported by thofe glafs 
flicks in a vertical polition, and is exceedingly well infulated. 
GH 1 LKM and NOPV are two frames of wood, which being 
fattened to the bottom boards, by means of brafs hinges, may 
be placed fo as to fland in an upright pofition and parallel to the 
tin plate, as lhewn in fg. 1. or they may be opened, and laid 
upon the table which fupports the inftrument, as lhewn in fg. 
2. The inward lurfaces of thofe frames from their middle 
upwards is covered with gilt paper XY ; but it would be better 
to cover them with tin plates, hammered very flat. When 
the Literal frames fland flraight up, they do not touch the tin 
plate; but they fland at about one-fifth part of an inch afunder. 
They are alfo a little fhorter than the tin plate, in order that 
they might not touch the tin tubes AD, BC. In the middle of 
the upper part of each lateral frame is a fraall flat piece of 
wood S and T, with a brafs hook ; the ufe of which is to hold 
up the frames without the danger of their falling down when 
not required, and at the fame time it prevents their coming 
nearer to the tin plate than the proper limit. It is evident, that 
when the inftrument (lands as lhewn in fig. 1. the gilt lurface 
of the paper XY, which covers the infide of the lateral frames, 
Hands contiguous and parallel to the tin plate. 
When 
