PRESSURE ON RESISTANCE OF METALS. 



631 



that the compressibility and thermal expansion of most metals change 

 lelatively little between 0° and 100°, the slope of the constant volume 

 line will be nearly independent of temperature. Since furthermore 

 the relation between temperature and resistance is nearly linear for 



TABLE XXII. 



Average Temperature Coefficients between 0° and 100° at kg. and 



12000 KG. 



most metals between 0° and 100°, the actual change in resistance in 

 ohms of a given piece of wire will be the same for 1° rise of temperature 

 at 100° as at 0°. But since the pressure coefficient is approximately 

 constant, the change of resistance for 1 kg. will therefore, be greater at 

 100° than it is at 0° in the ratio of the resistance at 100° to that at 0°. 

 For most metals this is of the order of 40% difference. Therefore the 

 slope of the line at constant resistance is greater at 100° than at 0°. 



