438 
MR. HARRIS ON THE ELEMENTARY LAWS OF ELECTRICITY. 
respective quantities are as 2 : 1. I have adverted to the results in Table IV. merely 
by way of illustration : it is however quite evident that with other intensities the 
coincidences alluded to might be more perfect, especially if, as in the experiment 
cited by M. Biot, we had, instead of a small disc, employed an insulated sphere of an 
inch in diameter fortesting the respective electrical reactions : in this case, as I have 
already endeavoured to show (19.), the disturbing force of induction would be more 
powerful, one of the repelling bodies having greater extension (Table V.). 
25. If, instead of previously charging the disc of the needle with the same electri- 
city, it remains neutral, and the electricity taken up by the proof plane be equally 
distributed between them, we may frequently avoid the disturbances above mentioned, 
more especially if the electrical intensities and the distances are within certain limits. 
Thus we observe, in again referring to Table IV., that in columns A and B, where 
the quantities on each disc are as 2:1, the forces are in almost every instance as 
4:1, the force being as the square of the quantity ; a result which I obtained also 
from the attractive forces by another and very different kind of experiment*. 
Experiment H. — With a view, therefore, of further verifying the preceding results, 
the former experiments, Table VI., were repeated in this way ; that is to say, the electri- 
city was distributed equally on the two discs and the square roots of the forces taken to 
designate the respective quantities : under these circumstances I found the electrical 
reactions of the charged sphere before and after contact both with the circular plate 
and with an equal sphere, in the ratio of 4 : 1 ; hence the quantity abstracted by the 
plate was equal to the quantity abstracted by the sphere, and just half the original 
quantity. I took in these experiments an electrical reaction of 16° distance as a unit 
of charge ; having previously ascertained by experiment that with this intensity the 
forces varied as the square of the quantity, or very nearly so, when the quantity on 
the discs was reduced to one half ; the reactive force of the instrument being about 
the Tr-jjVodth of a grain for each degree, and the proof plate of an inductive capacity 
adequate to the purposes of the experiment (42.). 
26. Although the above result seems sufficiently conclusive of the point under con- 
sideration, and is quite in keeping with the result arrived at in my former paper, viz. 
that the capacity of a sphere is the same as that of a circular plane of equal area into 
which we may suppose it to be expanded-!- : it may still not be altogether useless 
to verify it by another kind of experiment, equally conclusive and direct with the 
preceding. 
Experiment I. — The discs p m of the balance, figs. 3 and 14, being brought into con 
tact, and one of the insulated spheres above mentioned, S, fig. 9, connected with the 
fixed disc p , a charge was conveyed to it, which, on easing away the lever confining 
the needle, amounted to 48° at 48° distance. This being noted, the sphere S was 
touched with the insulated circular plate P, and the new position of the index from 
zero noted ; the disc of the needle was then touched with a similar neutral disc, so 
f Ibid. p. 235. 
* Philosophical Transactions for 1834, p. 219. 
