14 Trans. Acad. Sci. of St. Louis. 



A after fixing was not observable during the developing 

 of the film when it was viewed from above. It was seen 

 on turning the plate over so as to expose the under side. 

 This fogging had therefore been produced through two 

 glass plates. 



Plate VIII shows two photographic plates exposed 

 back to back in the same manner, when the negative dis- 

 charge was passed through the upper wire. From the 

 film of the lower plate B a negative discharge passed to 

 the grounded wire below. This downward discharge pro- 

 ceeded from an area which was coincident with that of 

 the blackened area on the upper film A. This is revealed 

 by the presence of small black points here and there to- 

 wards which fine discharge lines proceed, and from 

 which the discharge passed to the wire below. The form 

 of these lines seems to have been somewhat affected by 

 electro-magnetic induction from the discharge wire across 

 the upper film. The fogging effect on a film from which 

 electricity passes to a conductor, is much less than that 

 caused by a like discharge of electricity against the film. 

 It is this difference, which has always been ascribed to a 

 difference between positive and negative discharges. 



The exposure of plates like those shown in Plates III 

 and V, where the grounded wire was in place, was varied 

 as follows : 



A blast of air from a large tank of 800 liters capacity 

 and maintained at constant pressure of two and a half 

 atmospheres, was blown across the end of the grounded 

 wire below the photographic plate. The blast swept 

 through the gap between this end and the photographic 

 plate. This was done with both positive and negative dis- 

 charge. The blast was also directed along the discharge 

 wire in contact with the upper film. Not a trace of any 

 effect on the discharge lines could be detected, although 

 the blast was maintained throughout the entire exposure. 



The results thus far described seem to show conclu- 

 sively that the apparent emission of positive electricity 

 from the positive terminal of the influence machine, is 



