278 



Mr. H. Tomlinson. The Influence of [Jan. 26,. 



aluminium, were increased by temporary longitudinal stress. With 

 aluminium and nickel the specific resistances were diminished by stress 

 not carried beyond a certain limit. With nickel and carbon it was 

 necessary to introduce slight modifications of the original method of 

 determining the influence of stress on the resistance. With carbon, 

 though the increase of resistance produced by a given amount of 

 stress was greater than was the case with any of the other substances 

 except tin and lead, this was not so with respect to the specific 

 resistance. 



In the next table will be found the mean results of the different 

 experiments made with the various substances in the annealed con- 

 dition. 



Name of sub- 

 stance. 



Increase of re- 

 sistance per 

 unit produced by 



a stress of 

 1 grm. per square 

 centim. — sig- 

 nifies decrease of 

 resistance. 



Increase of re- 

 sistance per unit, 

 which would be 

 caused by stress 



sufficing to 

 double the length 

 of the wire. 

 — signifies de- 

 crease of 

 resistance. 



Increase per unit 



of specific 

 resistance which 

 would be caused 



by stress suf- 

 ficing to double 

 the length of the 



wire. — sig- 

 nifies decrease of 

 resistance. 





2111 x 10- 12 



4-180 



2-618 





2285 



3 404 



2 -252 





4406 



3 379 



2 113 



Tin 



10546 



2 -920 



1-630 





17310 



2-885 



1 -613 





4272 



3-851 



1 531 





2310 



2-713 



1 005 





9248 



2 -480 



0-980 



Platinum- silver . 



2346 



2-464 



0-624 



Grerman- silver . . 



1523 



2-018 



-226 



Aluminium .... 



1896 



1-276 



-0-262 



Nickel* 



-3216 



-6-994 



-8-860 



The numbers given in the above table are calculated on the assump- 

 tion that the alteration of resistance is proportional to the stress ; this 

 was found to be nearly, but not quite, the case. With most metals the 

 resistance increases in a greater proportion than the stress ; but with 

 iron which has been very heavily loaded for some time, the ratio of 

 the increase of resistance to the stress producing it after increasing to 

 a maximum begins to diminish ; and altogether, we may say, that the 

 results here obtained completely confirm those already recorded in 



* The numbers given opposite this metal are calculated from the results 

 obtained for stresses carried up to the above-mentioned limit, and as in the case of 

 the other substances, represent the alterations which would ensue if the changes of 

 resistance were proportional to the stress for any amount of the latter. 



