On the Generation of Statical Electricity. 97 
utility appears to have been discovered by accident, and whose real 
object seems to have escaped attention, has succeeded or failed, 
as chance regulated its proper or improper application. A certain 
quantity of electricity is doubtless produced by the silk, in what- 
ever manner it may be applied, and the amount is considerably in- 
creased by particles of amalgam which adhere to its surface ; but 
the total quantity thus produced is small compared with that given 
by the rubber, and a larger amount will be obtained by removing 
the flap and increasing the pressure, so as to bring as many new 
points in contact as will equal by their friction that of the silk. 
Hence the above cannot be its true value, neither ded its utility ap- 
pear to depend, principally, on its being an interposed non-conduct- 
ing obstacle between the excited glass and the molecules of air ; 
but rather, having been fastened to the loose edge of the amal- 
samated leather, this edge was pressed against the glass by the 
adhesion of the silk, and thus prevented from diminishing the 
amount of electricity already evolved. It possesses, also, to some 
extent, the power of preventing the electricity of the surface of 
the glass from being drawn off or neutralized by surrounding ob- 
jects. In modern machines, the rubbers are hair-stuffed cushions 
without the loose leather, and the flap is of varnished silk, which 
is so arranged, in some plate machines, as not to touch the glass. 
The first and principal advantage of the silk is thus lost, but the 
second more certainly obtained. 
From what has been stated, it appears to be important to cause 
that edge of the rubber which the glass last leaves in its revolu- 
tions, and which is covered with amalgam, to press constantly 
and firmly against its surface. This is best secured by making 
use of a leather strip, covered with the amalgam, whose edge in 
question shall be firmly pressed between the glass and cushion, 
and which is consequently narrower than the latter. The idea 
now suggests itself, that in thus contracting the rubbing surface, 
its action may be lessened ; hence, the proper dimensions for the 
rubber are next to be determined. ‘To solve this proposition, re- 
quires a further investigation into the phenomena of excitation. 
Statical electricity has been assumed to be produced by friction, 
and hence the result of molecular disturbance. ‘Taking one of 
the exciting points of the rubber, resting on a corresponding por- 
tion of the glass surface ; suppose such portion of the glass to 
move through an indefinitely small space ; molecular disturbance 
Vol. xx1x, No. 1.—April—-June, 1845. 13 
