RECENT PROGRESS IN PHYSICS. d©5 



the consequences arising from it. It remains obscure, precisely as he 

 conceived it. 



That the electricity of a powerful electrical machine can exercise no 

 perceptible inductive action through a partition wall and closed door 

 of a chamber, should certainly not surprise us, and can be of no value 

 as an argument against the view held by Fechner. 



In the course of the memoir alluded to above, experiments are de- 

 scribed which Fechner made to discover how electricity is distributed, 

 over an insulated and induced body. The essential results of these 

 experiments are as follows : 



A small Leyden jar, provided with a metal ball 

 A (fig. 25) 3 inches in diameter, was charged with 

 -f- E and insulated. Tlie ball was placed opposite 

 an insulated brass conductor a c b. This conduc- 

 tor was cylindrical, 5.2 lines in diameter, with 

 spherical knobs 8.3 lines in diameter at the ends, 

 and 16 inches long, a and A were placed 2 in- 

 ches apart. 



When the conductor was touched at a by the finger, a jn'oof-plane 

 constantly indicated negative electricity, to whatever part of the con- 

 ductor it might be applied ; even at h negative electricity was found, 

 the intensity, however, increasing towards a. Even from the finger or 

 hand touching the conductor, — E was obtained by the proof-plane. 



On the removal of the hand, so that the conductor a h became again 

 insulated, the greater part towards h indicated positive, the less part, 

 towards «, negative electricity. 



This result at first appears surpriiing, but it can be explained readily 

 by the following consideration : 



When the conductor is touched at a, — E, attracted by A, is accu- 

 mulated upon the hand, and, of course, acts repulsively upon the — B 

 in a. The repulsive action of the — E of the hand, and the attractive 

 action of the -j- E of the ball A, upon the — E present in a, are in 

 equilibrio ; but if the — E upon the hand be removed, more — E can 

 accumulate in a, a part of the neutral E of a h is tlien decomposed^ 

 the — E flows to a, while towards h is collected the -\- E repelled 

 by A. 



If, on tbe contrary, the conductor be touched at &, — E is indicated 

 throughout its entire length, increasing from h toward a, being, how- 

 ever, very feeble > at h ; on the removal of the finger, the whole con- 

 ductor becomes negative, increasing from & to a as might have been 

 predicted. 



The arrangement which electricity must assume upon a conductor 

 exposed to inductive influence, is reduced by Poisson to pure mathe- 

 matical determinations, which are based solely upon the known laws 

 of the attraction and repulsion of electricity. The practical application 

 of theprinciple, however, involves, in many cases, great difficulties; 

 for the comi)osition and decomposition of the actions are to be considered 

 from an infinite number of points. By general consideration, evidently 

 very little can be accomplished in a field where the obtaining of resulte 

 is too difiicult even for the calculus. In such cases it is necessary to 

 seek instruction from experiment. 



^ 25 s 



