﻿224 M. W. von Bezold's Investigations on the Electrophones, 



tricity which has passed to the lower surface can only come into 

 operation when the stronger electricity originally excited is 

 bound, after inverting the cake negative electricity can only so 

 long occur in the cover as the cake is near enough to the form, 

 while with increasing distance of the cake a position must be 

 reached at which the sign of the spark taken from the raised 

 cover changes. That this is the case is seen from the follow- 

 ing experiment. 



Fourth Experiment. — If the cake of an electrophorus which 

 has been strongly rubbed in the normal position be inverted and 

 laid with the rubbed side upon the form, the cover after being 

 touched and raised will yield negative electricity. But if the cake 

 be laid upon gradually higher supports, the quantity of negative 

 electricity furnished diminishes with extraordinary rapidity, dis- 

 appears completely at a certain distance between the form and 

 the cake, while at greater distances gradually stronger positive 

 charges occur. This can be admirably seen if, instead of an 

 electroscope, dust-figures are again used, if the cover after each 

 time of lifting be brought into contact with a conductor placed 

 upon a test-plate; for then continually decreasing negative 

 figures are obtained, followed by continually increasing positive 

 ones. 



Fifth Experiment. — The experiments previously instituted 

 have shown that when the electrifying is not excessive, no elec- 

 tricity passes between cover and rubbed surface, as indeed has 

 always been assumed, while it does pass from the unrubbed sur- 

 face and the form. This remarkable fact will be more easily 

 comprehended from the following experiment. 



If the cake be rubbed while it lies upon insulating supports, 

 and if it be then covered with an entirely unelectrified ebonite or 

 glass plate, and if then a conductor be placed upon this latter — 

 after dusting, positive figures will be seen upon this plate. These 

 become much smaller if the cake be laid upon the form. The 

 conductor might also be placed directly upon the cake ; but this 

 would in general yield no trustworthy results, since the shape of 

 the figure formed upon the part rubbed always depends on the 

 very varied excitation of the individual places. 



This experiment teaches that by the vicinity of the form, and 

 of course also by the positive electricity deposited upon the 

 surface B, the decomposing force which A can exert upon a 

 higher point is diminished. Hence a transition of electricity 

 takes place more readily between the cake and the form than 

 between the cake and the cover, which is only subsequently placed 

 upon it ; for the electricity originally excited is for the most part 

 bound by that on the form and the surface B. If the original 

 excitation was too powerful, the space between cover and cake 



