296 New Self-Registering Electrometer. 
fine stream soon breaking into drops; the water and vessel 
rapidly becomes charged with the same potential of elec-— 
tricity as the air at the point where the water breaks into 
drops. ifthe vessel be kept indoors, the insulation which it 
is necessary should be kept perfect, can be more easily main- 
tained. The pipe and nozzle may project through a window 
or any other opening into the open air. A conducting- 
wire attached to this vessel gives a means of con- 
veying to the electrode of the electrometer, either periodi- 
cally or continuously, the electric motive force as possessed 
by the stratum of air where the water drops from the 
nozzle. 
In the apparatus I have devised, the Leyden jar, metal 
protecting case and dried air are adopted in the electrometer 
and the water dropper for the collector, and it is only in the 
sensititive or movable part that it differs from those hitherto 
constructed. The sensitive part has always been suspended 
or held in position by a glass or silk fibre, or metal wire, and 
the force to be overcome by the electric force to be measured 
has either been torsion, as in Sir W. Thomson’s instrument, 
or the directive magnetic force of a small magnet, as in 
Peltar’s electrometer; in this instrument, however, the 
movable part is a delicately poised metronome pendulum; 
substituting for torsion or magnetism the more measurable 
and reliable force of gravity. I have styled it “The Pendu- - 
lum Electrometer,” and it may be thus described: 
On a heavy base of slate, two upright strong brass stems, 
about 18 inches long and 10 inches apart, are fixed connected 
at the top by a stout cross piece of brass ; at the centre of this 
cross piece and at right angles to it, a block of vulcanite is 
fixed, and to the under part of this again, and also at right 
angles to the cross piece two segments of a heavy ring of 
brass of about 44 inches radius are attached, so that they 
form together a true circular arch, but with the two seg- 
ments separated by about one-sixteenth of an inch at the 
vertex. (Plate ) These two segments insulated from all 
other parts and from one another constitute the electrodes of 
the apparatus. Between the two pillars a large Leyden jar 
is fixed to the base, with the mouth upwards. To the 
inside, bottom and inner coating of this jar a strong 
brass stem is connected, carrying at its top a brass frame 
with two arms, reaching above the mouth of the jar, 
which form the support of the pendulum. The pendulum — q 
consists of a light circular ring of brass (to carry 
