292 



Scientific Proceedings, Royal Dublin Society. 



The arrangement used for testing these samples is shown in fig. 2. T is 

 the sample with mercury electrodes ; M the megger ; a condenser with 

 mica dielectric ; E. V. an electrostatic voltmeter, Lord Kelvin's multicellular 



Fig. 2. — Diagram of the arrangement used for testing the samples. 



type ; G a galvanometer ; D a shunt-wound dynamo, whose field rheostat 

 was adjusted to give different voltages when required ; B a battery of about 

 100 volts; iTi and K 2 reversing keys. K l was made of four small cylinders 

 of paraffin wax, well separated, and mounted on a base of vulcanite, which 

 in turn was mounted on glass. Cavities at the top of the cylinders held 

 mercury. 



The three methods of testing were used for checking each other. This 

 may be done in the case of the megger and galvanometer methods, as their 

 ranges are more nearly alike ; but the range of the leakage method is to a 

 large extent outside that of the other two. 



Most of the results of this investigation were obtained by using voltages 

 of about 1 00 for the leakage method, and a capacity of 0'5 microfarad, or 



