- On the Generation of Statical Electricity. 105 
It is important that the elements of the glass, subjected to the 
action of the rubbers, be as long as possible ; for the glass surface 
may be considered as composed of an indefinite number of con- 
secutive portions, and as each one of these portions, when excited, 
acts inductively on those around it, it follows, that the greater 
the number excited at the same time, the greater must be the re- 
ciprocal inductive influence. Hence large machines, when un- 
der the same circumstances, must give electricity of a higher 
tension, than that produced by smaller rhachines. 
Having thus discussed the principles of action, of the various 
parts of the rubber, it remains to apply them practically. To 
obtain the narrow strip of rubber, requires the following process: 
being provided with a strip of common amalgamated leather, 
subject it to strong pressure, in order to render the surface flat and 
smooth ; it is then to be rubbed with a clean cloth, to remove 
any excess of lard or tallow, if such substances be employed ;* 
which must still further be removed from the exciting points, 
by rubbing the amalgam with a piece of smooth leather dipped 
into mercury, to which a few particles will adhere; this not only 
cleans the exciting points, but enlarges their extent. 
If the amalgam be now applied to the glass with pressure, 
those portions of the surface still covered with the lard or tallow, 
might come into contact at some points with the surface, and 
produce a detrimental effect ; to avoid this, reduce some plum- 
bago (black lead) to a fine powder, which is to be rubbed over 
the surface of the amalgam, and by adhering to such portions 
will render them excitable points. It also permits greater press- 
ure for the same amount of friction; and thus the surface is 
brought more intimately into contact with the glass. From 
the leather prepared as above described, a strip one fourth of an 
inch broad, and somewhat longer than the rubber, is to be cut; 
carefully avoiding to break up the amalgam at the edges, which 
may be accomplished by covering it with pasteboard and cutting 
through both substances. 
The rubber proper being prepared as above directed, it remains 
to apply it to the cushion, which, to avoid unnecessary resistance, 
should be three quarters of an inch or one inch in breadth, and 
this last dimension should not be exceeded in the largest machines. 
A * Wax and shellac, as previously stated, may be used with adrenal; but they 
require more care in the manipulation 
Vol. xix, No. 1,—April-June, 1845. 14 
