144 



BEPORT 1892. 



In order to show that at the same temperature the resistance always 

 returns to the same value — in other words, that there is no hysteresis in 

 the relation between those two quantities, some points of the curve were 

 determined with temperatures descending from 70° C, whereas others 

 were obtained with ascendir.g temperature. This process was repeated 

 several times. The spots marked / correspond to descending, the spots 

 marked ^ to ascending temperature, and the points belonging to the 

 same series of observations have the same sign. All points are extremely 

 close to the same continuous curve, and it is quite obvious that this 

 curious behaviour is a constant physical quality of the material. Of 

 course such a resistance-coil must have been artificially aged before the 

 beginning of the observations ; it was indeed heated during live hours at 

 a temperature of about 140° C. Otherwise, as I mentioned before, a 

 progressive process of decrease of resistance through annealing would 

 superpose upon the regular variation of resistance according to the curve. 

 It is true that this maximum resistance-point does not always occur at 

 exactly the same temperature for wii'es of different size ; it is well known 

 that the electrical constants of all resistance alloys change slightly with 

 the gauge of the wire. But it is also true that the maximum resistance- 



FiG. 2. 



point of manganin of a thicker size — say 1 ram. — occurs, as a rule, afc 

 about 30° C, and so at ordinary temperatures the temperature-coefficient 

 is even less than for this particular specimen of wire. 



The material is very soft, and can be drawn to the finest gauges ; but 



