352 



Scientific Proceedings, Royal Dublin Society. 



Table 14. 

 White erinoid ; Thickness 0475 cm. 



a = 140 E. 



The results obtained for this sample on the second day agree very well 

 with those found on the first day. 



The results of Tables 9, 12, 13, and 14 are plotted in Tig. 4, and the 

 curves show that the thinner the erinoid the higher is its specific resistance. 

 This characteristic is confirmed by the results for unmachined black erinoid 

 in sections 1 and 2 of Table 2 — namely, a = 65,000 for a thickness - 248 cm. 

 at 16-8° C, and 26,000 for a thickness 0-53 cm. at 16-6° C. 



In the latter case the greater part of the large difference in <r was probably 

 due to some difference in the manufacture of the thin and thick sheets. 



This characteristic, also possessed by certain other materials, may be due 

 to a large skin effect, or a large contact resistance between the material and 

 its mercury electrodes, or a combination of both causes. 



In the case of the machined white erinoid, in addition to the preceding 

 causes, there may have been a greater drying out in the thinner sample, due 

 to its drilling and turning, and also to its heating in the test. 



The inset curves of Fig. 4 support the view of either skin or contact effect, 



