loos, Mr. wilson’s Experiments 
that either of them could be made longer or fhorter, juft 
as the experiment required. On the end of one of the 
prongs was fixed a ball of brafs, three quarters of an 
inch in diameter, and on the other a fharp fteel point or 
needle. The fhoulder of this fork fcrewed into a fmall 
plate of iron that was fixed on the infide of a wooden 
veflel, which contained the greateft part of a cylindri- 
cal glafs jar twelve inches and three quarters high, and 
about four inches in diameter. This glafs was rather 
thick than otherwife, and the coating of it (which 
was tin-foil) meafured nearly 144 fquare inches on? 
each furface. Befides this coating, part of the infide 
of the wooden veflel was coated alfo with tin-foil,, 
for the purpofe of making a fecure communication 
between the iron plate and the outward coating of the 
jar. Within the jar itfelf was fitted a cylinder of 
wood, that was covered with tin-foil alfo, to make a com- 
munication between the infide coating of the glafs and a 
brafs rod that was fixed upright in the center of the 
wooden cylinder. This upright rod having a ball of 
brafs at the end, three quarters of an inch in diame- 
ter, was bent towards the firft part of the circuit: fa- 
that the two balls A and b in plate xvm. fig. 2. being 
upon a level* looked towards each other, but were 
placed 
