410 



Scientific Proceedings, Royal Dublin Society. 



absorbed water took place, but this, on weighing, was found to be practically 

 negligible. 



On testino-, it was determined that there was no appreciable creepage 

 over the tops of the walls of the sample, and the resistance was independent 

 of the applied voltage : two essential conditions for representative measure- 

 ment of insulation resistance. The former was shown to be the case by- 

 measuring the resistance of the tube for a given level of the mercury contact- 

 surfaces, and then changing this level and again measuring the resistance. 

 The specific resistance calculated for different levels was found to be very 

 nearly constant. The voltage test up to 500 was performed by the galvano- 

 meter and the voltmeter method. 



Each set of resistances for different temperatures, measured after an 

 interval of immersion in moist air, was tabulated as in Tables 3 and 4. 

 These two tables are typical of each of the twenty-seven sets obtained; 

 Table 3 being for black vulcanized fibre after 63 hours' immersion in moist 

 air, and Table 4 for red erinoid after 6'5 hours' immersion. 



Table 3. 



Table 4. 



t being the temperature in degrees centigrade, T the absolute temperature, 

 and R the resistance of the sample in megohms. 



