r 374 ] 



XLIX. Liquid Coherers and Mobile Conductors. 

 By Eollo Apple yard*. 



IN a communication f made three years ago to the Physical 

 Society, I described some experiments illustrating the 

 change in electrical resistance of certain complex bodies under 

 the influence of oscillatory discharges. All the substances 

 dealt with were solids ; and the coherence was invisible. The 

 change of condition had therefore to be demonstrated either 

 by measuring the resistance before and after discharge, or by 

 connecting the coherers permanently in series with a battery 

 and galvanometer. 



The three experiments now brought before you have regard 

 to " coherers" formed of liquid dielectrics, and mobile con- 

 ductors. By choosing a transparent dielectric and an opaque 

 conducting substance, it is possible to examine the process of 

 coherence by direct observation. But it may be well to 

 premise that the similarity of results obtained with solid and 

 liquid " coherers/' respectively, in no way proves a similarity 

 of process. The two sets of phenomena are probably related, 

 but are not necessarily identical. The term " dielectric " is 

 here to be understood as signifying merely a substance of low 

 conductivity. 



Experiment 1. — A glass tube about eighteen inches long, 

 and haif-an-inch wide, is sealed at one end and corked at the 

 other. Platinum electrodes are inserted at each end. The 

 tube is nearly filled with about equal volumes of paraffin-oil 

 and mercury. If it is laid upon a flat table and shaken, 

 horizontally, for a few minutes, the mercury breaks up into 

 small spheroids ; and, by a little manipulation, these can be 

 disposed as a chain of particles lying evenly between the 

 platinum electrodes. The resistance of the chain of mercury 

 spheroids, measured under these conditions, is several 

 megohms. 



If we now connect the electrodes to a battery of about 

 two hundred volts, the whole regime is suddenly altered. 

 At the moment of applying the current, the spheroids of 

 mercury, within the tube of oil, are visibly impelled, as 

 though a mechanical tap had been administered to the glass ; 

 and, almost simultaneously, they coalesce into large globules. 

 The resistance is now represented by a few ohms. 



Exactly the same result can be brought about by sup- 

 porting the tube near a Hertz oscillator; or, still more 

 simply, by passing a spark into one or other, or both, of the 



* Communicated by the Physical Society : read March 26, 1897. 

 t "Dielectrics," Phil. Mag. xxxyiii. p. 396 (1894); Prcc. Physical 

 Society, xiii. p. 155 (1895\ 



