Gill — E feet of Electric Current on Photographic Plates. 75 



iu the way presently to be described. As a rule the whole series was 

 employed, but definite results were obtained with a few cells in series. 

 Tlie feeble results obtained by this method were sufficiently definite to point 

 to certain conclusions wliich seemed worth examining under circumstances 

 which would produce more strongly marked reactions. The experiments 

 were therefore repeated, making use of damp photographic plates and a 

 series of small storage-cells. As the results obtained in tliis second series of 

 experiments include, with increased distinctness, all those which had been 

 observed in the original investigation, I have confined my description to 

 them. 



Method of making Hie experiments. — The plates were soaked in clean water 

 for five or ten minutes, and were then pressed for a moment between sheets 

 of clean blotting-paper to remove any superfluous water from front and back. 

 The electrodes, which I shall call anode and kathode, were coins or other 

 pieces of flat metal connected by wires to the terminals of a battery of 

 storage-cells giving a potential difference of 400 volts. These coins were 

 placed on the gelatine surface of the plate and kept in position by means of 

 wooden clips. -The ' exposure ' occupied about ten minutes. The plates 

 were then developed in the ordinary way. In this paper the figures 

 represent the plates as they appeared on development, so that the blackened 

 portions of the original photographic plates are black in the figures. 



Effect produced at the kathode. — In the experiments on dry plates no 

 effect was observed at the kathode — a fact which had its counterpart in the 

 experiment now to be described. In general the effect produced at the 

 kathode did not depend on the nature of the metal employed, and was 

 less marked than that at the anode, but was present even when no 

 blackening was produced at the anode. As will be seen from the figures, the 

 kathode effect consists of a number of ray-like projections stretching out on 

 the side facing the anode, being much less, or altogether absent, on the more 

 distant side. This was accompanied by a slight blistering of the moist 

 gelatine surface, as if gas had been liberated. The blistering was visible 

 before development, but the change of colour did not appear until the plate 

 had been developed (Plate I., fig. 1).' 



General effect at anode. — The effect at the anode is much more marked than 

 that at the kathode, though not always resulting in a blackening of the plate. 

 This effect is characteristic of the nature of the metal used as electrode, and 

 appears to consist of two reactions, both of which are not always observed. 

 One of these reactions, which appears to be common to all metals, and which 

 does not of itself result in a blackening of the plate on development, may be 



' All the figures are full size. 



m2 



