[ z°3 ] 
In the next place, I repeated this experiment by 
balancing the two different methods of communi- 
cating electricity to the circuit, one againft the other. 
For, not infulating the jar, but fetting it on the table, 
which gave the circuit and the bodies contiguous to 
it an advantage for contracting pofiuve electricity by 
the difcharge ; but, at the fame time, making an. 
interruption in the circuit (by introducing part of the 
table into it, which tended to give them negative 
eleCtricity) ; I could eafily manage it fo, that the 
circuit contracted neither the one nor the other; 
and yet, as in the former cafe, the lateral explofion 
was as coniiderable as ever. The balls never fepa- 
rated. 
To vary the experiment, I placed an infulated 
brafs ball, two inches in diameter, round andfmooth, 
fo as not eafily to part with any eleCtricity it had 
got, in the place of the rod that fupported the pith 
balls ; and having found a fituation in which no 
electricity was communicated to the circuit, I ob- 
lerved that none was communicated to it, though, to 
ail appearance, it received a {park of about L of an 
inch in length. At lead, if it had contracted any, 
it was fo little, as to make it very problematical ; 
whether a pith ball, or a fine thread, was moved by 
it, or not : whereas, when 1 gave it the fmallefl 
fenfible fpark in any other manner, it would attraCt 
thofe light bodies for a long time together. 
The interruption of the circuit 1 made ufe of in 
this experiment, was not by means of any part of 
the table, but only about a yard of brafs chain in- 
troduced into it, and difpoled between the infide of 
the jar and that part of the circuit, near which the 
D d 2 infulated 
