Miscellaniés. 405 
abraded rubber itself, adheres to the firm part of the latter, chiefly 
at the last stage of the rubbing, by an electrical attraction, and ac- 
cordingly, when the hand is passed lightly over the rubber, the adher- 
ing matters drop off, because the hand conducts away the electricity. 
When a piece of India rubber is pressed closely upon the brass 
cap at a Bennet’s gold leaf electrometer, and suddenly withdrawn, 
will diverge and strike the sides of the glass 5 ; if the rub- 
mply stretched and applied, the excitement is feeble, espe- 
cially z slowly withdrawn, “while a smart separation causes the 
leaves to diverge at once to their greatest extent.” The production 
of heat, when a thong of caoutchouc is held against the lips and sud- 
denly pulled to the utmost, and at the same moment pressed hard, i is 
well known. 
According to Dr. J. K. Mitchell, the caoutchouc, even in the ex- 
treme thinness to which he reduces it by his peculiar mode of ex- 
panding it, by blowing after immersion in ether, entirely prevents the 
passage of the electric spark from the prime conductor ; it is how- 
ever probable that it would be lacerated by the discharge from a 
eres battery. 
The remainder of Mr. Johnson’ S paper, we quote entire. 
“The fact, however, that it has a power of resisting to a consider- 
able extent, points it out as a good medium to be interposed between 
the two surfaces of the condenser, or substituted in some form for 
the Leyden phial. 
“For this purpose, a piece of gum, reduced to a very thin sheet, 
may be interposed between two sheets of tin foil and laid upon a ta- 
ble; a thicker sheet of gum may then be laid upon the upper sheet 
of oa, so that the edge of the latter should be at some distance from 
that of the former. "The whole may then be rolled up into a coil, 
allowing a small part of the included tin foil to project out at one 
end of the roll. A charge may now be given to this apparatus, and 
a shock obtained by connecting the outer sheet of tin with the part 
of the inner, projecting at the en 
“A disk of metal may be ctivered with a thin sheet of caoutchoue 
and another disk furnished with an insulating handle placed above it; 
this apparatus will serve all the purpose of the ordinary condenser. 
| “1 have stretched a piece of gum upon a circular piece of board, 
| six inches in diameter, with a coat of tin foil underneath ; on rubbing” 
this with flannel, it becomes highly ie 4 x and if a plate, like the 
Vou. XX.—No. 2. - 
