NUOVE NOTIZIE STORICHE SULLA VITA E SULLE OPERE DI MACEDONIO MELLONI 



37 



I do not think that our ignorance of the essential nature of the electric force offers any dif- 

 ficulties in the consideration of the nature of induction, conduction, etc, provided we do not 

 travel beyond facts and the laws which govern them. 



In induction, it is only the surface of the conductor which is finally affected, and not 

 its internai parts : and that whether the conductor be insulated or connected with the earth 

 (1220, 1221, 1295, 1301). If it be uninsulated, only that part of its surface is finally affected, 

 on which lines of induction force, proceeding from the exited or inductric body A, abut and 

 terminate : if it be insulated, then the parts of the surface, from which an exact equivalents 

 of new lines of force originate and proceed outwards from the compound system (fig. 2) 

 towards neighbouring conductors, are afl'ected also : the first surface is B, the second surface C 

 and the neighbouring parts, and between them there is a part or zone, of various from ac- 

 cording to circumstances, in the neutral or normal conductor. 



The induction is limited by the induction surfaces (1231, 1297, 1361, 1372, 1483, etc). 

 The one which is primarily charged I bave distinguished as the inductric, the other at the 

 inductors. 



The lines of induction force, used merely as representations of the disposition of the electric 

 force, are described (1231, 1304, 1441, 1450): they commence at one and terminate as the 

 other, of the inducting surfaces. If the inductric body A be an exited insulator, as a rod of 

 shell lac, they then commence at the exited particles. 



Induction is not sustained through the body of the thinnest conductor. Theoretically, it 

 occurs at the first instant: but conductors discharges its state within, and it is the surfaces 

 only of the conductor which remains finally affected. An uninsulated gold leaf in a frame or 



Fig. 1. Fig. 2. Fig. 8. 



ring, may have its opposite sides raised by induction to the highest opposite or like states, 

 without the slightest interference of one side with the other. 



The lines of induction force across the dielectric or insulating medium may be curved (1215, 

 1219, 1221, 1224, 1230, 1374, 1449, 1614. See also figures 7, 8, 9, 10, 11, 12). Ih experiments 

 in open spaces they are almost universally curved. 



Induction lines have a lateral relation (1224, 1295, 1449) quite analogous to that of the 

 lines of current force, when the piles of a voltaic battery are dipped apart from each other into 

 a large mass of water or dilute solutions; and which have been so well illustrated by Nobili 

 in bis metallochromic results. 



When a charged sphere A (fig. 3) is in the center of a much larger sphere of conducting 

 matter, the lines of force proceed as radii from A to every part of the outer sphere: the sum 

 of force on the surface of A and the sum of contrary force on the inner surface of the sur- 

 rounding sphere, are exactly equal to each other. 



When an insulated conductor B, C, is introduced, then a certain amount of the lines of 

 force from A terminate on B, produces an opposite state there, but an equal amount of force 

 or of lines, originate about C and terminate on D ; or in other words the lines of force which 

 would have been passed across the space B C, if the conductor B C were away, have, through 

 the conduction of the particles of B C, been replaced by the equivalents of contrary forces 

 at the respective surfaces of B and C; at the same time, as the resistance or tension set up 

 in induction (1368, 1370, etc), is removed as regards the space B C, by the conduction; so, 

 more electricity must induce from A towards B than in other directions, as towards E; and 

 more inductions action is induced on D than elsewhere as at E. But though D differs thus 



