372 EXPERIMENTAL INVESTIGATIONS. 



contact can be produced without contact, and by mere ap- 

 proximation, the intermediate dielectric being polarised, or a 

 radiation analogous, if not identical, with that which produces 

 the images of Moser taking place from plate to plate. 



The present experiments also associate themselves with 

 the gas battery, where, though an electrolyte is used as the 

 means of making the action continuous, or producing what is 

 called current electricity, the initiating effect is gaseous polar- 

 ity, the films of gas in contact with the respective plates of 

 platinum having antithetic chemical and electrical states. 



The results detailed in Experiment 13 appear to open a 

 new field of research. Priestley observed concentric circles 

 produced by the electrical discharge from a powerful Leyden 

 battery, which he describes as consisting of minute cavities 

 and globules of fused metal* In my experiments there is an 

 alternation of oxidation and reduction, a medium capable of 

 producing both being present ; the lateral effect and comple- 

 mentary colours have to my mind something closely resembling 

 the phenomena of interference in light, although, from the 

 polar character of the force, it is difficult to imagine any pre- 

 cisely analogous condition of electricity. The discharge 

 taking place from different parts of the needle, and extending 

 from its point to a considerable distance over its surface, 

 would give different lengths for the lines of polarisation and 

 discharge to the different parts of the disc on the silver plate 

 affected by the discharge ; and assuming electricity to be pro- 

 pagated by undulations, there would be interference ; but 

 instead of alternations of light and darkness we get alterna- 

 tions of positive and negative electricity. The ring of polished 

 metal between the central spot and the exterior ring quite 

 distinguishes these rings from the ordinary colours of thin 

 plates, i.e. colours the annular succession of which depends 

 only on the different thicknesses of the film ; here doubtless 

 the colours of the oxidated portions are colours of thin plates. 

 Experiment 14 shows clearly that the action by which the 

 polished ring is formed is a polar action of the discharge, and 

 not a mere absence of action. 



* History of Electricity, 2nd edition, p. 624. 



