a Conductor the Measure of the Current passing. 359 



little uncertain; but its character is well defined. In the 

 diagram the abscissae are the percentage corrections to be 

 applied to the resistance for each degree by which the air 

 temperature differs from 15°. The resistance thus corrected 

 is the value for an air temperature of 15°. 



Fig-. 5. 



1-2 

 1-0 

 0-8 

 0-6 



n.d. 



























> 









n 



ZSi 









0-2 

 





j 







COEFFICIENTS 





0-1% 



0-2: 



0«3& 



0-4% 



12. The results of experiments on the degree of exhaustion 

 of the vessel are given in the diagram of fig. 6. It will be 

 noticed how rapidly the resistance for a given current, 

 1*2 amperes, air temperature 15° C, increases with the 

 exhaustion when the latter is fairly perfect. This might 

 form the basis of a useful gauge for high vacua. In the next 

 set of experiments the vacuum was actually gauged in this 

 way, the pumping being started before each set of readings 

 and continued until the resistance ' of the strip for a given 

 current, 1 ampere, corrected for the air temperature from the 

 figures of fig. 5, took the same value as before. The curve 

 at normal atmospheric pressures is too steep to be of any use 

 as a barometer. 



13. On the diagram of fig. 7 are plotted a number of 

 observations made on four different occasions of the resistance 

 of the platinum strip of fig. 4 ; the vessel being exhausted 

 to about -2 inch mercury, the exhaustion being fixed by the 

 resistance at 1 ampere. 



