136 



BRIDGMAN. 



the manganin pressure gauge, so that a very accurate comparison of 

 the pressure coefficients of manganin and Therlo could be made by 

 plotting on a large scale the difference of the readings with the two 

 alloys. The Therlo was seasoned by one application of 12000 kg. at 

 room temperature, and after soldering to the insulating plug, by four 

 additional applications of 2000 kg. 



Three runs were made, at 0°, 51.05°, and 94.80°. The variations 

 with temperature were so slight that the readings could be reduced to 

 regular temperature intervals by an interpolation or extrapolation so 

 short that there was no possibility of error. The resistance of this 

 sample of Therlo did not vary quite linearly with pressure, that is, 



(0 



•? 

 a 



E 



.0,4 



.0,2 

 .0,0 





0° 20" 40° 60" 80° 100° 

 Temperature 



0-^ 20" 40" 60" 80° 100" 

 Temperature 



Pressure, Kg. / Cm. X 1 



Comet 



Figure 12. Results for the measured resistance of Comet alloy. The 

 deviations 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. 



it did not vary linearly with the manganin. (The manganin was 

 originally calibrated against an absolute gauge and found linear within 

 0.1%). The deviations from linearity of the Therlo are greatest at 

 the lower pressures and are not symmetrical. 



At 0° the maximum departure of any single observed point from a 

 smooth curve was 0.09% of the total pressure effect, at 51° 0.14%, and 

 at 95° 0.05%. 



The results have been computed in the regular way, and are exhib- 

 ited in Table XIX and Figure 13. The method of representation is 

 the same as that used in the preceding paper on resistance under 



