154 



BRIDGMAN. 



The results are collected in Table I and Figure 1. The method of 

 presenting these results is the same as that of the previous papers. 

 The average pressure coefficient between and 12000 kg. is that 

 number which multiplied by 12000 gives the change of resistance pro- 

 duced by 12000 kg. pressure as a fractional part of the resistance at 

 atmospheric pressure and the temperature in question. The instan- 



1 /nn\ 



taneous coefficients at and 12000 kg. are — ( — 



R\dp, 



resistance at the pressure and temperature in question. The maxi- 

 mum deviation from linearity is in fractional parts of the resistance 

 at 0° and atmospheric pressure. As an example, suppose that it is 

 required to find the resistance of aluminum at 50° at 6000 kg. in terms 

 of its resistance at 0° and atmospheric pressure as unity. The average 

 coefficient at 50° to 12000 is — 0.0 5 4129, and the initial resistance at 



where R is the 



40° 60° 



Temperature 



40° 60° 80° 

 Temperature 



Al 



uminum 



Figure 1. Aluminum, results for the measured resistance. The devia- 

 tions from linearity are given as fractions of the resistance at kg. and 0° C. 

 The pressure coefficient is the average coefficient between and 12000 kg. 



50° is 1.2334. If the change of resistance with pressure were linear, 

 the decrease of resistance under 0000 kg. would be 1.2334 X 6000 X 

 0.0 5 4129 or 0.03056. But the change of resistance is not linear, but 

 as the sixth column shows, there is a deviation from linearity at 6000 

 of 0.000S6, giving for the total decrease of resistance under 6000 

 0.03142, and for the actual resistance at 50° under 6000, 1.2020. 



Compared with the results for the previous sample, the pressure 

 coefficient of this is in general higher by eight or nine per cent. As a 

 function of temperature, the pressure coefficient of this new sample 

 shows a very flat maximum near the lower end of the temperature 

 range, and from here on decreases. The pressure coefficient of the 

 other sample decreased linearly over the entire temperature range. A 

 decrease of the coefficient with increasing tempera tine is not what one 

 might at first expect, but its reality seems vouched for by independent 



