Experiments and Inductions. 203 



(24, 25, 26.) Here there is evidence, especially in 25., that 

 the flame or match acts in discharging the B. D. partially, as if 

 unconnected with the electroscope. In this it differs from the 

 action of points, which could not discharge the B. D. without 

 charging the electroscope, although the discharge would of 

 course be more limited than if the plate of the electroscope were 

 a free conductor. 



(27, 28.) Why should not the brass disk be discharged under 

 the same conditions that discharge the excited sulphur ? 



(30.) This is proof of induction acting in curved lines, 

 which Faraday was the first to direct attention to (Experimental 

 Researches, 1218, 1231). Not entertaining the possibility of 

 such curved action taking place in a vacuum, he holds that the 

 inductive force is enabled to bend round in consequence of the 

 molecules of air being polarized, and one leading the action 

 to the others in straight lines. In § 63 of paper in Phil. 

 Trans, for 1834, Harris states that the operation of electricity 

 on distant bodies by induction is quite independent of atmo- 

 spheric pressure, and is precisely the same in vacuo as in air. 



(31.) The free part of the charge which issues from the exterior 

 surface of the inside coating gradually diminishes, and the 

 engaged or masked portion between the coatings consequently 

 expands, and the free part comes to issue from the exterior sur- 

 face of both coatings. So the electroscope shows latterly the 

 action of that nearest to it, which again is removed by touching 

 the outer coating. See 34. 



(35.) The diminution of the excitement probably takes place 

 by discharge (the exact nature of which remains to be discovered). 

 This must take place, not only on the excited side, but all over. 

 Now remark that the discharge of the electric lines that takes 

 place on the excited side is the total of each line discharged ; 

 but the discharge that takes place on the side opposite the 

 excited side is the discharge of lines that pass through the cake, 

 so it must leave undischarged that part of each line that lies 

 between the two surfaces, having negative root on a and positive 

 on /3. A charged magic pane without coatings is thus gradually 

 formed and gradually also discharged. It is the engaged lines 

 becoming gradually disengaged that at last brings out the posi- 

 tive electricity on the surface opposite to that originally negatively 

 excited. 



(37.) The inductive effect on a wax surface is very marked in 

 this and other experiments. If a B. D. charged negative is 

 placed resting on a cake of sulphur, it induces gradually a per- 

 sistent positive on that part of the surface of the sulphur upon 

 which it rests. Time is required. See 39, 40. 



(38.) When first discharged this double cake has positive on 

 P2 



