Effect of Electrical Convection. 



43 



discharged, and even though there should be a slight leakage 

 of a real charge across to the surface of the disk, this charge 

 could produce no deflexion of the galvanometer, as the charge 

 would tend to assume a constant value, whereas the deflexion 

 of the galvanometer is due to a change in the electrical con- 

 dition of the disk. 



For this experiment two ebonite disks were made, diameter 

 30*5 cms., thickness "8 cm. The gilded micanite disks used 

 in the first experiment were replaced by these (see fig. 2). 



Fig. 2. 



I 



u 



I + 



The two condensing plates C 2 and C„ 

 next to the induced coil I were earthed. 

 The other two condensing plates C : and 

 C 4 were connected through the inter- 

 rupter to the pole of the Voss machine, 

 so that they might be rapidly charged 

 and discharged. Everything else re- 

 mained exactly the same as in the first 

 experiments. When the two outer 

 plates Cj and C 4 are charged positively, 

 for example, the two ebonite disks 

 become polarized, so that the surfaces 

 next to the outer condensing plates 

 assume an apparent negative charge, 

 and the surfaces nearer the inner con- 

 densing plates C 2 and C 3 assume an 

 apparent positive charge. Since the 

 positively charged surfaces are nearer 

 the induced coil than the surfaces 

 negatively charged, when the outer 

 plates are suddenly discharged while 

 the disks are rotating, there will be a 

 slight current induced in the coil I. 

 Since the two surfaces oppose each 

 other in their magnetic action the 

 resultant effect is very small, being 

 greater the thicker the disks, for the 

 same surface-density of the apparent 

 charge. A slight deflexion of the 

 galvanometer was observed with the 

 disks arranged as just described, but 

 it was found that a greater effect could 

 be obtained by mounting the two disks flat up against each 

 other on the same axle, thus using only one side of the ap- 

 paratus. This arrangement amounted to the use of a single 

 disk 1*60 cm. thick, i. e. twice the thickness of one of the 

 disks. Also it was possible to charge to a higher potential 



J 



^Actual Size 



