Induction in curved Lines — in Air. 



357 



might be expected from an inductive action in straight lines, 

 but that obtained at b is not so : it is clearly a charge by in- 

 duction, but induction in a curved line-, for the carrier ball 

 whilst applied to b, and after its removal to a distance of six 

 inches or more from B, could not, in consequence of the size 

 of B, be connected by a straight line with any part of the 

 excited and inducing shell-lac. 



1220. To suppose that the upper part of the uninsulated ball 

 B, should in some way be retained in an electrified state by that 

 portion of the surface which is in sight of the 

 shell-lac, would be in opposition to what we know 

 already of the subject. Electricity is retained 

 upon the surface of conductors only by induction 

 (1178.); and though some persons may not 

 be prepared as yet to admit this with respect 

 to insulated conductors, all will as regards 

 uninsulated conductors like the ball B; and 

 to decide the matter we have only to place the 

 carrier ball at e (fig. 4.), so that it shall not 

 come in contact with B, uninsulate it by a 

 metallic rod descending perpendicularly, in- 

 sulate it, remove it, and examine its state: it 

 will be found charged with the same kind of 

 electricity as, and even to a higher degree 

 (1224'.) than, if it had been in contact with 

 ofB. 



1221. To suppose, again, that induction acts in some way 

 through or across the metal of the ball, is "" 

 negatived by the simplest considerations ; 

 but a fact in proof will be better. If in- 

 stead of the ball B a small disc of metal 

 be used, the carrier may be charged at, or 

 above the middle of its upper surface ; but 

 if the plate be enlarged to about li or 2 

 inches in diameter, C (fig. 5.), then no 

 charge will be given to the carrier atj^ 

 though when applied nearer to the edge at 

 g, or even above the middle at /z, a charge 

 will be obtained ; and this is true though 

 the plate may be a mere thin film of gold- 

 leaf. Hence it is clear that the induction 



is not through the metal, but through the air or dielectric, 

 and that in curved lines. 



1222. I had another arrangement, in which a wire passiu'i- 

 downwards through the middle of the shell-lac cylinder to the 

 earth, was connected with the ball B (fig. 6.) so* as to keep it 



summit 



Fig 5. 

 ® 



