1909-10.] Observations on some Spark-Gap Phenomena. 223 
manner of the “ electrical chimes ” experiment, by alternate charge and 
discharge, attraction and repulsion. This pendulum motion could be shown 
in its most regular form by staying down the plate lightly with another 
silk bifilar.] Preconceived theories of this repulsion, such as that of a 
possible hydro-electric excitation of the surface of the plate by the dis- 
charge,* are upset when we, once more, employ electrodes of different 
shapes. Thus if the sphere and cone be again used, it does not then 
matter which is + and which — : the repulsion is always violent, and in 
the direction from the conical electrode to the spherical one, regardless of 
polarity. If the electrodes are not opposite one another, then, on reaching 
the sphere, the plate is rotated through a considerable angle (fig. ii.). If 
the plate is not allowed to touch either electrode, but is tested immediately 
— on -4- 
F rcj. .11 . 
after the discharge, it shows always the sign of the conical electrode. 
When the electrodes are similar, it shows always the sign of the repelling 
electrode, i.e. +. Another curious phenomenon occurs in the case of 
similar electrodes, e.g. spheres. Let the plate be repelled against the — 
electrode, and remain there during discharge. If the electrodes are not 
opposite one another, it will again show rotation, but this time of the 
opposite sense to that in fig. ii. That is to say, it behaves as if attracted 
simultaneously by both electrodes, but with the — electrode in pre- 
dominance (see fig. iii.). This effect could not be obtained with metal 
plates : it may hence be inferred that different parts of the dielectric plate 
are in this case in different electrical conditions as regards charge. 
III. If the plate be light enough, and the electrodes placed so near the 
edge of the plate that the path of least resistance for the discharge is 
* Doubrava also disposed of the hydro-electric theory by using as the plate a thin sheet 
of some dielectric or conductor, enclosed in an envelope of material of the opposite hydro- 
electric sign, and showing that the effect remained unaltered ( Wiedemann Annalen, 
loc. cit.). 
