Xvl On t 1,:)e Method of rendering very fen fib le 
u you touch with the knob of it the metal plate of our con- 
denier, when properly fituated f viz. upon an imperfeftly con- 
ducLing plane, &c.) and immediately after take up the faid 
P . e ’ thls w iU he found to give very confpicuous figns of elec- 
tricity, which (hews that the Leyden phial is not quite de- 
prived of electricity as it appeared. But if the phial was left 
io far charged as juft to attract a light thread, then if the metal 
plate were to be touched by the knob of it, even for a moment 
it would afterwards, when lifted up, give a ftrong fpark, and if 
then it were to be touched again by the knob of the phial, it 
would afford a fecond lpark hardly fmaller than the former, 
and thus fpark after, fpark may be obtained for a long time, 
which is a very furprizing experiment. 
This method of producing fparks by means of a phial, which 
is not charged fo high as to give fparks of itfelf, is very conve- 
nient for various pieafing experiments ; as, for inftance, that of 
lghting tne inflammable air-piftol, or lamp, contrived by me. 
especially when a perfon is provided with one of thofe phials’ 
prepared after the manner recommended by Mr. Tiberius’ 
cavallo *, which when charged may be carried in the pocket 
for a long time. Thofe phials, as they retain a fenfible charge 
toi feveral days, will retain an in fenfible one for weeks or 
months. I mean, by an infenfible charge, fuch as cannot be 
fo covered but by the help of the condenfer, in which cafe it 
becomes more than fenfible, and fuffleient for the experiment 
of the inflammable air-piftol, &c. 
25.. Secondly, Suppole you have an eledrical machine fo 
ba .„v 111 or< for that its conductor will not afford any fpark, but 
will juft attraft a thread; then if you let this conductor touch 
the metal plate of the condenfer, and after fuffering it to 
continue m that fituation for a few minutes, whilft the machine 
[1 ’ c P t 111 m °tion, lift up the metal plate, you will obtain 
from it a ftrong fpark. 
26. Thirdly, In cafe, the eleftrical machine atfs very 
ueh,. but its conductor is fo badly infulated, that it will 
nol give any fparks, as when the conductor touches the walls 
Sec his Treatife on Electricity, 
Of 
