442 
MR. HARRIS ON THE ELEMENTARY LAWS OF ELECTRICITY. 
upon the indications of this instrument, termed a proof plane, all the experimental 
evidence of the theory of electrical distribution in charged bodies of various forms 
depends. 
35. Without embarrassing the inquiry by any theoretical disquisition, let us study 
the phenomena as they immediately present themselves. There exists in electricity, 
as already observed, a peculiar kind of influence termed induction, not recognised in 
other invisible natural agencies, magnetism excepted ; that is to say, the attractive 
force displayed by these wonderful powers is invariably accompanied by a previous 
change in the electrical or magnetic states of the attracting bodies. If, as in the ease 
of electrical attraction, the forces thus generated, as it were, by induction, be suffi- 
ciently powerful to overcome all impediment to the free communication of electricity, 
these induced states are found to vanish, and a new disposition of the accumulation 
immediately takes place, and it is thus one body receives electricity from another, 
I hope at an early period to lay before the Royal Society some new phenomena in 
electricity calculated to throw further light on the operations of electrical induction 
and attraction, and from which it would appear that the attractive force between a 
charged and insulated body in a neutral state, is entirely dependent on the reciprocal 
inductive forces of which, under the given circumstances, both the bodies are sus- 
ceptible, and not necessarily on the mere quantity existing on the charged body. 
The free electricity therefore which a small proof plane takes up from a charged body 
may not only depend on the quantity actually existing in any given point to which it 
is applied, but on the reciprocal inductive force of which the bodies are susceptible at 
such point of application. Should the inductive capacity of the proof plane become 
in any way affected by position, or by its thickness, or extension of any kind, or 
should the charged substance be itself more or less susceptible of induction in dif- 
ferent points, then the inductive forces will be different, and the attraction generated 
between the charged body and the proof plane not always proportionate to the actual 
quantity of electricity present, as can be shown by many striking experiments. The 
proof plane would not under these circumstances take up in every situation a quantity 
of electricity proportionate to that of the element of the surface to which it is applied. 
That something of this kind takes place, may, I think, be made evident in the fol- 
lowing way. 
Experiment N. — Take three equal and similar circular metallic plates, p,p',p", figs. 24, 
25,26. Let two of them, p' ,p”, be hollowed up into shallow spherical segments; insulate 
these bodies in the positions shown in the figures, the convexity of the segment p' 
being placed uppermost, and that of p" downward ; charge these insulated conductors 
with the same quantity of electricity, which may be readily effected by the methods 
explained in my former paper*. Now the respective intensities, as measured by the 
connexion of the charged bodies with any electrometer, are all equal -f- (28.) ; hence 
there cannot possibly be any exception taken on account of a supposed double sur- 
* Philosophical Transactions for 1834, p. 218. t Ibid. p. 233. 
