236 MR. HARRIS ON SOME ELEMENTARY LAWS OF ELECTRICITY. 



the least beyond the interior, as in fig-. 21, becomes immediately electrified when the 

 sphere is charged with electricity. 



61. We have yet to notice another seeming exception to the general law (16.) ob- 

 servable in accumulating variable quantities of electricity on insulated conductors, 

 and which is found to occur in that peculiar kind of accumulation induced in a body 

 by electrical influence. 



Many striking facts lead us to conclude, that excitation by induction, as above 

 stated (4. 5.), is the immediate effect of a tendency of accumulated electricity to a 

 given state, or mode of existence : hence an electrified substance is observed to exert 

 a peculiar kind of influence upon surrounding bodies. The immediate result of this 

 influence, is a sort of temporary change, or displacement, of the electricity which 

 these bodies already possess ; so that if they be insulated, a species of accumulation 

 is apparent in certain parts of them, depending upon a new disposition or state of 

 their own electricity. Now the attractive force thus induced in a neutral substance, 

 by the immediate influence of a charged conductor, appears to be as the quantity of 

 the free electricity in operation directly, that is, as the intensity or exciting cause; 

 and as the simple distance between the points of the opposed bodies inversely, which 

 may be gathered from the following experiments. 



(■$.) Two conductors, h h\ fig. 15, terminating in plane surfaces, as in fig. 22, being 

 insulated on the stand fig. 15. above described (33.), one of them, h, was connected 

 with the electrometer, fig. 2, and the other charged with a given quantity (14.), 

 whilst withdrawn from the influence of the former. These two conductors were now 

 placed within a known distance of each other, and the induced force in h observed : 

 after numerous repetitions of this experiment, the distances between the conductors 

 being varied, I found, that the force induced in the distant extremity of h was in the 

 simple inverse ratio of the distances between the opposed surfaces. 



(t.) When the distance was constant, and the accumulated quantity in h' variable, 

 then the induced force in h varied with the square of the accumulation in h' directly. 



62. I repeated these experiments with the balance, and with an electrical jar, ac- 

 cording to the method already explained (19.), fig. 9, and found the result invariable. 

 In this latter case the conductor h was immediately connected with the jar by a straight 

 wire, and h' with the insulated ball b, so as to interpose the conductors between the 

 jar and the balance, the distance between the opposed surfaces being adjusted by the 

 micrometer-screwy, fig. 15. 



63. Assuming in these experiments, what is quite consistent with strict philoso- 

 phical reasoning, that every effect is directly proportionate to its cause, we have ad- 

 ditional evidence of the law already deduced (16.) ; since to excite an attractive force 

 in a distant body, varying as the square of the quantity of electricity accumulated in 

 the exciting conductor, the free quantity, or intensity, in the latter must at least vary 

 in the same ratio ; hence it follows that with a double quantity accumulated there is 

 four times the intensity, or free action. 



