450 
MR. HARRIS ON THE ELEMENTARY LAWS OF ELECTRICITY. 
plate becomes g reatly diminished as its length is increased, although the area of the 
plate and the quantity of electricity remain the same ; a subject which I have already 
treated of to some extent *. But in extending a plate in length, we elongate, as it 
were, the stratum of electricity resident about it, and thus place the electrical mole- 
cules, if such exist, in a new relation of position in respect of each other and of the 
general surface of the plate. If so apparently trifling a change as the extension of 
an electrified plate in length, the area not being diminished, is capable of diminishing 
the attractive force of the charge so much as to reduce it nearly in an inverse ratio of 
the length ■f', it is not unreasonable to suppose that the position of the proof plane, as 
respects the mass of the electrical molecules, may have an important influence on its 
indications. 
Suppose, for example, the square plate a d, fig. 28 , to be charged with electricity, 
and to a given intensity ; imagine its area to consist of thirty-six equal squares, each 
an inch square, the side of the plate being six inches ; then if we imagine the same 
area to become placed under the rectangle a d\ thirty-six inches in length, and only 
one inch in width, the thirty-six small squares will, as is evident, assume another 
arrangement in respect of each other. Any one square will be in contact with only 
two others, they will have, as it were, at least two sides free, whilst those at the ends 
o' d ' will have three sides free. Now in the square a d, each of the smaller squares is 
placed between four others, except those at the edges, which have one side free, and 
those at the angles, as at a and d , which have two sides free. 
It is always difficult, in treating of so incomprehensible an agency as electricity 
through the medium of effects, to avoid altogether certain hypothetical analogies and 
forms of expression : it will be however understood that in resorting to such analo- 
gies, they are to be considered merely as philosophical contrivances, introduced for 
the purposes of illustration, and not in any way subservient to an exclusive theory of 
electrical action. 
Under this necessary limitation, let us imagine the distribution of the electricity 
upon the square a d, to be, in the absence of any other conducting body within 
the sphere of its influence, uniform. Then, as is proved by experiment^:, the capacity 
of the area ad is increased when it becomes placed under the rectangle ad; we can 
hence place a greater quantity on the plate d d, under the same intensity, than on 
the square a d. Imagine a proof plane to be applied to the square ad at the centre c. 
and to be in the state of any other insulated neutral body placed, under ordinary cir- 
cumstances, very near it, without becoming identified with an element of the sur- 
face : then the same cause, whatever it be, which affected the capacity of the square 
a d , considered as a whole, may also affect the capacity of the proof plate considered 
as a whole. We may infer, for example, that at the centre c the electrical particles 
to which it is immediately applied are enveloped on all sides by other particles, and 
that hence none of the sides are free. When, however, we remove the plate to the 
* Philosophical Transactions for 1834, p. 232. + Ibid. p. 233. + Ibid. p. 232. 
