482 



ScienfAfic Proceedings, Royal Duhlin Society. 



obtained for the rigidity of about 0'2 per cent. ; and in measuring the 

 diameter of the wire a standard micrometer screw-gauge was used, in which 

 an error in reading of -g-^mm. made an error of 0'3 per cent, in the value of 

 the rigidity, so that the values of the rigidity obtained may be reckoned 

 correct to within the half of one per cent. ; the same error in estimating the 

 diameter of the wire would cause an error of about the half of one per cent, 

 in the value of the electrical conductivity ; both methods were therefore used 

 as a check on one another. 



The results are collected in Table I., and shown as curves in fig. 1 

 The rigidity is expressed in grammes per square centimetre, and the 

 electrical conductivity as a percentage of pure copper. 



Table I. 



Cross-sectional 

 area of the 



wire 

 X 10"^ sq. cm. 



20-80 

 20-73 

 20-64 

 20-46 

 20-35 



Rigidity 

 X lO" 



Ho 

 H, 

 Ha 



H3 



803 

 812 

 823 



Electrical 



conductivity 



pure copper, 



100. 



14-3 

 14-0 

 13-6 

 12-5 

 9-1 



to -5 



Fio. I. — Load on wire (grammes per sq. cm. x 10^) when it was heated. 



