﻿M. W. von Bezold's Investigations on the Electrophorns, 217 



covered with red lead. But in this case we have the incalculable 

 advantage that this result is not obtained merely for one single 

 point as by the direct application to the electroscope, or as 

 the mean value of a larger surface is obtained with the plane, but 

 that the electrical deportment of each individual point of ex- 

 tended surfaces may be seen at a glance. Moreover the peculiar 

 arrangement of this powder enables us to draw a tolerably safe 

 conclusion as to the seat and the origin of the quantities of elec- 

 tricity in operation. 



A rubbed surface after being sprinkled exhibits bands which 

 indicate the direction of the rubbing. If electricity has passed 

 to the disk by a spark, peculiar dust figures are obtained ; and 

 after glimmering discharges, spots of dust. If, however, it is 

 a case of action at a distance, larger portions of the surface are 

 found uniformly covered with one and the same powder. The 

 least action exerted by the disturbing influence of adjacent bodies 

 (a point, &c.) is at once perceptible to the eye ; and any one who 

 will take the trouble to repeat with a good (polished) ebonite 

 plate the experiments subsequently described, will be astounded 

 at the simplicity and precision of the means mentioned and at 

 the beauty of the phenomena. He will also at the same time 

 be convinced that the results obtained with the means hitherto 

 employed, just on account of such local disturbances, must always 

 be liable to great uncertainty. 



From this point of view the following very instructive experi- 

 ments may be made, which afford an excellent opportunity of 

 studying the points here mentioned. 



If on one surface of an ebonite plate which rests upon insula- 

 ting supports, and is beyond the sphere of action of points, a 

 positive spark is passed by means of a needle, after sprinkling, 

 a yellow star is obtained upon the upper surface. Upon the 

 lower one, on the contrary, a yellow spot with indistinct edge is 

 obtained, the magnitude of which is about equal to that of the 

 star. If near the lower surface there was a point or a flame, an 

 indistinct red spot is observed on this surface. If, finally, the 

 plate lay upon a metal plate in connexion with the ground, after 

 the sprinkling on the lower surface a well-defined red spot is 

 formed, the extent of which is less than that of the positive star 

 — that is, a negative Lichtenberg's figure. In the first case elec- 

 tricity was only active on the upper surface, which indicated also 

 on the lower surface its presence by action at a distance only. 

 In the second, negative electricity had really passed to the lower 

 surface, but only by a glimmering discharge, in the third, how- 

 ever, by a spark-discharge. 



If an insulating surface to which a powerful discharge passes 

 be covered with a perfectly unelectrical insulating plate (ebonite 



