436 
MR. HARRIS ON THE ELEMENTARY LAWS OF ELECTRICITY. 
been touched with an insulated circular plate, one of whose surfaces was equal to 
the exterior surface of the sphere, it exhibited only one third the reactive force which 
it evinced before the contact, and hence concluded that the quantity remaining on 
the globe after the contact, was only one third of the previous quantity ; that conse- 
quently the charge had divided itself between the plate and sphere in the proportion 
of their assumed surfaces of action. 
22. It may not be unimportant to examine the claims of this evidence, since it has 
necessarily considerable influence on the future progress of electricity. 
In the detail of Coulombe’s experiments, given in the Traite de Physique of Biot. 
the result of the contact of the plane and sphere does not appear to have been com- 
pared with any result of contact with a similar sphere ; that is to say, with the elec- 
trical reaction of the original sphere when an equal sphere was substituted for the 
plate. According to his views, the reaction after one contact of the plate should 
equal the reaction after contact with a similar sphere, whose exterior surface was 
equal to the two surfaces of the plate. This experiment, after what has been just 
stated, is essential to an accurate result ; since it is possible, that although the elec- 
trical reactions shown by the balance of repulsion may be nearly as 3 : 1, yet still the 
actual quantities of electricity may be only as 2 : 1 (15.). Not finding in any of the 
accounts of Coulombe’s inquiries which have come under my notice an experiment of 
this kind, it may be worth while to commence with this test of the theory. For this 
purpose I obtained two conducting spheres, each four inches in diameter, and a cir- 
cular plate of eight inches in diameter, as represented by S, s\ P, fig. 9. 
Experiment G. — Having insulated and charged one of the spheres, S, as also the 
disc of the needle, with the same electricity, according to the method of experiment- 
ing adopted by Coulombe, I proceeded to ascertain its electrical reaction by means 
of a tangent disc, and found the needle repelled 22°, the reactive force of the instru- 
ment being about the -a -oVo dth of a grain for each degree. The charged sphere was 
now touched with the insulated plate P, and its electrical reaction again observed. 
This being effected, I replaced the original charge on the sphere, so as to again 
obtain a force of 22°, and then repeated the experiment with the second insulated 
sphere s. The results are given in the following Table, in which it may be seen that 
the electrical reactions, after the respective contacts with the plate and sphere, the 
areas of which were equal; instead of being as 2 : 1, according to the theory, are 
nearly the same, whilst the subsequent forces at 22° distance, as compared with the 
reaction of the original charge of 22° at the same distance, are nearly as 3 ; 1 . This 
ratio we have found in several instances where the charges on the repelling discs are 
unequal and in the ratio of 2 : 1. 
