ON THE SPECIFIC RESISTANCE OF METALLIC WIRES. 375 
77 per cent. per 1 per cent. of elastic elongation, and after stretching 15 per 
cent. the variation becomes 7 per cent. per 1 per cent. increase of length. 
Table IV. No. 2 gives a variation of 3°3 per cent. per 1 per cent., and 
No. 3 36 per cent. per 1 per cent. of elongation for that specimen of iron, 
while from Table V. we obtain the successive variations, 4°8, 4°7, 4°8, 4°6 per 
cent. per 1 per cent. of elongation. 
Table VI. No. 3 gives four determinations of the variation due to elastic 
elongation, from which it appears to pass through a maximum after a certain 
degree of permanent elongation, and then again diminishes as the elongation 
is increased. The values obtained in this case were 0°75, 1°04, 0°86, and 0°71, 
the corresponding permanent elongations being 9°20, 11°71, 15°73, and 16°59 
per cent. The results which I have given for the effect of elastic elongation 
after different degrees of permanent elongation must be considered as strictly 
preliminary. The arrangement I had made for the purpose of observing the 
effect of permanent elongation was not sufficiently sensitive to give very accu- 
rate results for elastic elongation, but I think them sufficiently accurate to 
indicate that there is a change, and the direction of that change. I hope by 
rearranging the apparatus, and removing the pulley over which the wire passes, 
so that the elongations can be inferred from Hooxe’s law, and by increasing the 
resistances CC, to obtain a series of reliable results on this latter part of the 
subject. 
TABLE I.—Specimen of Japanese Copper. 
: Percentage 
Weight on | Percentage | Increase of : Number of 
ae yd Ae Hidnpation. Specific 2a Experiment. 
i Resistance. 
13th April, . : . 10° 0:000 0-000 3c¢ No. 1. 
os c ; . 14: 0:89 0:59 obe Sic 
os 16:25 1:68 1:12 
» 185 2°57 1°75 
> 21 3°58 2°26 
=p ; ; - 21 5°05 3°32 
(gheApril) 1. +: 5) ‘Obs 671 3-65 
15th April, . : : 10:00 0:00 0:00 noe No. 2. 
hee : : : 21:00 1:23 0°82 ere Sac 
» 22°5 2°01 1:13 
» 23°5 3°06 1:56 
» 24:5 3°49 1:66 
” 26 4:07 2:18 
5 27 5:07 2°66 
» 28 6°33 3°41 
: : c 29° 7:20 3°56 
16th April, . 3 ; 35°5 8:58 4:84 
Fs ‘ é : 37° 9:03 4°80 
. c c ‘ 37° 9:90 5:14 
