Obfervations on TLleffricity . 277 
refpe&s which I have not thought fit to alter. When the five- 
inch ball gives flafhes, the cylinder is enveloped on all fides 
with fire which rufhes from the receiving part of the con- 
ductor. I never ufe points, but in a fimple machine bring the 
conductor almoft in contaft, with the cylinder. In this appa- 
ratus that cufliion to which the rubber is not applied ferves 
that purpofe. 
24. Thefe marks exhibit the intenfity as deduced from fim- 
ple electrifying. I will now mention the rate of charging, 
which was nearly the fame in all the three cylinders. 
A large jar of 350 fquare inches* or near 2§ fquare feet, 
with an uncoated varnifhed rim, of more than four inches in 
height, was made to explode fpontaneoufly over the rim. The 
jar, when broken, proved to be 0.082 inches thick on an ave- 
rage ; and the number of fquare feet of the furface of the 
cylinder which was rubbed, to produce the charge of one foot, 
was, when ieaft, 18.03, ail< ^ when moft, with good excita- 
tion, 19-34. The great machine at Harlem charges * a (ingle 
jar' of one foot fquare by the fridtion of 66.6 fquare feet, and 
charges its battery of 225 fquare feet at the rate of 94.8 fquare 
feet rubbed for each foot. The intenfity of electricity on the 
furface of the glafs is therefore confiderably lefs than one- 
fourth of that here fpoken of ; but if we take the moil: favoura- 
ble number 66 3 6 at the commencement of turning, and halve 
it on account of the unavoidable imperfection of a plate ma- 
chine (as (hewn in par. 1 4.), it will be found, that the manage- 
ment applied to that machine would caufe a cylinder to charge 
one fquare foot by the friCtion of 334 fquare feet. It muft be 
obferved, however, that M. van Marum’sowii machine, con- 
* To explode from the central wire, which, from fome trials, I find to require 
lefs force than from coating to coating at equal diftances. 
. Vol. LXXIX. S f fitting 
