ON STANDARDS FOR USE IN ELECTRICAL MEASUREMENTS. 



143 



The alloy, which is now being regularly manufactured and brought 

 out under the name of manganin, consists of 84 per cent, of copper, 

 12 per cent, of manganese, and about 4 per cent, of nickel. As the 

 observations made by nie for the last two years in the Reichsanstalt have 

 shown, this is a most appropriate material for standard resistances. 



The general character of the resistance- variations of manganin with 

 temperature may be best understood from the diagram (fig. 1), in which 



Fig. 1. 



OhjfL. 



700,030 



tocmo 



/00.0W 



roo.ooo 



3^990 



W ZO' 30- *0' M' 



Tcmpe-T'cutLLre- «*»— 



60' 



70° e 



temperatures are taken for abscissEe, and the resistances of a hundred-ohm 

 standard are plotted as ordinates. In this case up to 40° C. the tern- 

 perature-coefEcient is positive, the absolute value, however, being very 

 small, as the following table of the mean linear coefficients between the 

 temperatures stated in the first column shows : — 



Table VI. 



For most purposes the variability of resistance with temperature may 

 now, indeed, be quite neglected. As a matter of fact, very elaborate and 

 sensitive methods are required to demonstrate the existence of any 

 temperature-coefficient at all. On raising the temperature beyond 60° C. 

 the resistance attains a maximum, thence to diminish again. In this 

 latter part of the curve we therefore actually have a negative temperatui-e- 

 coefficient. 



