96 Sir W. Snow Harris’s Researches in Statical Electricity. 
of the electrical force of the element of the surface which it actu- 
ally covers. 
18. These facts being duly considered, it appears by no means 
improbable that the distribution of an electrical charge through 
the medium of metallic surfaces, considered as conductors merely 
to the charge (10), may, upon the whole, be uniform,*or nearly 
so, and that the deduction upon the evidence of the proof-plane, 
that it is far otherwise, is at all events questionable. According 
to the action of the proof-plane, the electrical charge accumulated 
upon a long rectangular plane R, fig. 12, would be represented 
by a curved line, such as ahd, a large portion of the charge 
being accumulated at the extremities. It is, however, just pos- 
sible, on the other hand, from the phenomena observed, (14), 
(15), that the charge may be at least thicker at the centre, and 
admit of being represented by another kind of curve, such as 
dce*. If, however, we take the evidence of a simple and direct ex- 
periment, we should be led to conclude that the stratum of elec- 
trical charge upon the surface of electrified conducting bodies 
was uniformly distributed throughout. The following are a few 
striking and new experiments which greatly favour this conclu- 
sion, or are at least in accordance with it. 
Ezp.10. RB, fig. 18, is a rectangular plate of copper, about 4 
feet in length and 3 inches in width, carefully insulated in the 
way already described (2). The suspended or moveable disc 2, 
of the hydrostatic electrometer HE, is brought immediately over 
any point of the surface. The base of the vertical column D, 
sustaining the wheelwork, &c., is set on a travelling carriage or 
rail so as to admit of the whole being easily moved backward 
or forward, and the suspended dise n of the electrometer easily 
transferred immediately over any required point. Let R be 
now charged with any given measured quantity of electricity, 
so as to bring the index ¢ by the attraction of the disc n toa 
given point, say 10 degrees; the dise n being at a given di- 
stance above the plane, say an inch. Let the attracted disc be 
now gradually moved along over the surface of the plane from 
one extremity to the other ; not any appreciable change will ensue 
in the position of the dex; the force on the disc will be every- 
where the same,—a result perfectly consistent with the hypothesis 
of uniform distribution. Any simple apparatus may be employed 
for. this experiment, such as a common balance so poised as to 
admit of a small inclination without oversetting; or a vertical 
arm of light reed with pith-balls set ona delicate central axis, as 
shown in fig. 14, in which c is an insulated metallic cylinder, 
* It is worthy of remark, that in Beccaria’s experiments of the collection 
of the smoke of colophonia upon an electrified cube, the smoke “lay 
higher on the flat parts of the cube than on the edges and corners,” 
