630 



BRIDGMAN. 







10 



20 30 40 50^ 60' 70 

 Temperature 



80' 90 100 



Figure 25. Collection of results, the average pressure coefficient between 

 and 12000 kg. as a function of temperature. The seven curves in the lower 

 part of the diagram without labels are, reading upwards, for tungsten, molyb- 

 denum, tantalum, nickel, copper, platinum, and palladium. 



pressure. As a matter of fact, the temperature coefficient of all sub- 

 stances is only slightly different at 12000 kg. from its value at kg. 

 Now, dropping the condition of invarial)ility, it is easy to see that if 

 the pressure coefficient of resistance increases at higher temperatures 

 the temperature coefficient will be less at higher pressures, and vice- 

 versa. In Table XXII are collected the average temperature coeffi- 

 cients between 0° and 100° at and 12000 kg. for all the substances 

 for which the data have been obtained. Except for the abnormal 

 metals, the slight change in temperature coefficient is striking. 



The meaning of a temperature coefficient independent of tempera- 

 ture may be stated in another way. Let us compare at 0° and 100° 

 respectively the slope of the lines on which resistance is constant with 

 those on which volume is constant. Since it is a matter of experiment 



