54 M-. cavallo’s Account of 
other, by gently and alternately elevating and deprefling 
its extremities. This operation immediately renders the 
cutfide of the tube electrical, but with the following re- 
markable property, viz. that part or end of the tube 
where the quickfilver actually Hands is pofitive, and the 
remaining part negative. If* by elevating this poiitive 
end of the tube a little, I let the quickfilver run to the 
oppofite end which was negative, then the former in- 
flantly becomes negative and the latter pofitive. The 
pofitive end is always more ltrongly eleCtrical than the 
negative. If when one end of the tube (which we call a) 
is pofitive, that is, if, when the quickfilver is in it, I do 
not take off the eleCtricity ; then on elevating it lb as to 
let the quickfilver run to the oppofite end b, the end a 
becomes negatively electrified in a very fmall degree: 
if I make it pofitive a fecond time, and do not take off 
that pofitive eleCtricity; then, on elevating it again, it 
appears to be pofitive in a fmall degree : but if whillt it 
is pofitive I take off that pofitive eleCtricity, then on being 
elevated it appears ltrongly negative. 
Thefe appearances I would explain in the following 
manner: the quickfilver agitated within the cavity of the 
tube aCts like a rubber, that is, excites the infide furface 
of the tube pofitively, and becomes itfelf negative. Now 
when the quickfilver, negatively electrified, is on one 
end 
i 
