Observations on some Experiments in Electricity. 67 
at the greatest possible distance,—that is at the whole length of the 
diameter,—from each other, the intensity is at a maximum. ‘To 
prove this we have only to employ the common plate machine with 
four rubbers on which the collectors are placed at two opposite points 
on the circumference, each a quadrant from one pair of the rubbers. 
A machine thus arranged yields a very copious supply of electricity 
and will charge a battery with great rapidity, but owing to the proxi- 
mity of the rubber to the collector, the charge is in some measure 
condensed,—the stratum of air between the two, serving a purpose 
analogous to that of the glass in the Leyden jar. If however we re- 
move the collecting points from their usual position, and also detach 
one pair of the rubbers and substitute a collector in their place, we 
shall discover, at once, a remarkable difference in the working of the 
machine, while it furnishes a far less rapid accumulation of electricity 
in a battery, the sparks will be greatly increased in intensity. By a 
change such as is here described, I have caused a machine, which 
was yielding sparks of only three inches, to extend them immediate- 
ly to eight inches and eight-tenths i in length, the gas balls, and 
insulators remaining, in both cases, the same. 
9. A method of producing rotation, 
The following experiment furnishes an illustration of continued ro- 
tary motion derived from electricity, different from that of flies with 
recurved points. 
Near the lower edge of a vertical plate machine four feet in di- 
ameter, of which the rubbers are on a level with the axis, I place on 
an insulating stand, a sharp pointed pivot, to receive a brass wire, or 
needle, five inches long which may revolve freely in a horizontal 
plane, like a common compass needle. The wire is furnished with 
a hollow brass ball at each end, half an inch in diameter. This nee- 
dle, of course revolves in a plane at right angles to that of the plate, 
and is placed so far only from the latter that the balls will not inter- 
fere with it when the two revolve simultaneously. For the purpose 
of this experiment the collecting points and prime conductor of the 
machine, ordinarily placed at the vertical points of its periphery, are 
removed. On turning the plate the needle with its balls begins at 
once either to revolve, or to oscillate through considerable arcs. In 
the latter case the oscillation is in a short time converted into a com- 
plete rotation, that soon increases in rapidity to two or three times a 
second, according to the action of the machine. Now ifa fly-wheel 
