70 Mr. F. S. Spiers on Contact Electricity, 



near that margin ; for there is hut little change in the initial 

 intensity of the sound-vibrations from the neighbourhood of 

 the central portion. To observers who are situated near 

 the continuation of the line of fault, the maximum epoch of 

 the sound will therefore precede that of the shock ; while to 

 those who are near the minor axis of the isoseismals, the two 

 epochs will approximately coincide. 



IV. Contact Electricity. 

 By Frederick S. Spiers, B.Sc'., A.C.GJ* 



§ 1. HP HE object of this investigation was to determine, in 

 J- a more satisfactory manner than has hitherto been 

 attempted, the part that the medium plays in the P.D. 

 that is observed between two dissimilar metals wdien they are 

 metallically connected. No experiment on this important 

 point, whether made in vacuo or in any gas whatsoever, can 

 be considered decisive unless the films of air condensed on the 

 two plates of metal be first removed. If the Volta effect is 

 due to the air at all, it is most certainly due to that part of 

 the atmosphere immediately surrounding the metals, namely, 

 to the condensed surface-layers of air or oxygen ; and hence 

 it is in the highest degree essential to be certain of the entire 

 removal of this surface-layer before any experiments can be 

 considered decisive. The molecular attraction between a 

 metal and the gaseous film in close contact with it is probably 

 of very considerable magnitude ; hence it is useless simply to 

 surround the metals with another gas, and then assume that 

 your measurements are being made in that second gas, 

 ignoring the original condensed sheet of air. 



Most experimenters on the subject have either ignored 

 altogether or else failed to realize in full the presence and 

 possible action of these air-sheets condensed on the metals, 

 A critical and, I may add, wholly delightful account of the 

 work done prior to the year 1884 is to be found in the 

 exhaustive report presented by Prof. Oliver Lodge to the 

 British Association in that year. Nobody will venture to claim 

 finality for any experiment bearing on the subject that is 

 described in that report. Neither can it be said that any work 

 published since that date effectually and decisively clears up 

 the many doubts and difficulties with which this matter 

 bristles. There are, however, two important researches con- 

 cerning which a few remarks here would not be out of place. 



* Communicated by the Physical Society : read Nov. 10th, 1899. 



