66 BRIDGMAN. 



Before this explanation can be finally accepted, experimental con- 

 firmation in several respects is required. Temperature measurements 

 should be made on the high temperature phase above the temperature 

 of transition. The resistance relations should be carefully studied in 

 the neighborhood of the transition point for nickel of high purity. 

 Finally it ought to be possible to recrystallize a wire by proper heat 

 treatment so as to make it into a single large crystal. Under these 

 conditions the character of the phenomena should entirely change. 

 The initial effect of tension should be normal, and should continue 

 so until a tension is reached so high as to force the transition to take 

 place, when there should be a discontinuous drop of resistance greater 

 in amount than the previous increase. Of course it is not obvious or 

 necessary that the tension of this discontinuity be less than the elastic 

 limit, and hence it may not be possible to realize it. 



Summary. 



The tension coefficient of resistance of lithium, calcium, strontium, 

 antimony, bismuth, manganin, and therlo has been determined. 

 These substances are all abnormal in that their pressure coefficients 

 of resistance are positive. Young's modulus for these metals has also 

 been determined. The tension coefficient for bismuth and strontium 

 is found to be negative, but positive for the other five. In the dis- 

 cussion I have shown that these coefficients are in accord with my 

 theory of resistance. The conduction mechanism of lithium, calcium, 

 antimony, manganin, and therlo is on the whole " transverse," that of 

 bismuth is longitudinal, and that of strontium is a combination. 



The negative tension coefficient found by Tomlinson for nickel 

 has been verified for nickel of high purity, and in addition the hystere- 

 sis effects and the effect of changes of temperature has been studied. 

 Cobalt, on the other hand, is found to be entirely normal. It is sug- 

 gested that the explanation of the abnormal behavior of nickel may 

 be found in a depression by tension of the transition point normally 

 at 360°. 



The Jefferson Physical Laboratory, 

 Harvard University, Cambridge, Mass. 



