t 403 ] 
XXVI. A Defcription of an Infirument which, by ihe turning cf 
a Winch , produces the T wo States cf Eleftricity without 
EriLtion or Communication with the Earth. In a Letter 
from Mr. William Nicholfon to Sir Jofeph Banks, Bart . 
P. R. S. 
Read June 5, 1788. 
SIR, 
- F HE following account of the inftrument I had the 
honour to fhew to yourfelf and other philofophical 
friends, in the month of March laft, will, I hope, appear 
fufficiently interefting to be communicated to the learned So- 
ciety, over which you fo worthily prefide. 
Plate VI. fig. 1. reprefents the apparatus fupported on a 
glafs pillar 6f inches long. It confifis of the following parts. 
Two fixed plates of brafs, A and C, are feparately infulated 
and difpofed in the fame plane, fo that a revolving plate B may 
pafs very near them, without touching. Each of thefe plates is 
two inches in diameter ; and they have adjusting pieces behind, 
which ferve to place them accurately in the required pofition. 
D is a brafs ball, likewife of two inches diameter, fixed 011 
the extremity of an axis that carries the plate B. Befides the 
more efifential purpofe this ball is intended to anfwer, it is fo 
Vol. LXXVIII. H h h loaded 
