ELECTRIFICATION OF AIR, VAPOUR OF WATER, AND OTHER GASES. 227 



84. We found also that as the air became rarer it was not so much electrified. 

 This was shown by the electric filter and electrometer. Thus the electrometer deflec- 

 tion for a pressure of 360 millims. was only about one-sixth of that for 760 millims. 

 with the same number of strokes of the pump, and the same potential of the electric 

 machine. 



Curves 11 to 16. 



is 



J7 

 16 

 IS 

 14 

 13 

 12 

 II 



10 





 

 ' 



6 

 5 

 4- 



i 



L 





7 



iooo aooo 



3000 4000 5000- 6000 



Voits 



7000 -8000 9000 10.000 



85. We next kept the pressure of the air in the bell-jar constant and varied the 

 electric potential of the electrifying needle. In this manner we found how much the 

 current through the air in the jar was increased by increasing the potential. The 

 curves 11 to 16 represent the relation between the potential of the needle and the 

 current from the needle-point through the air to the metal of the bell-jar, for certain 

 definite air-pressures, and for positive and negative electrification. It will be noticed 

 that for the same air-pressure the current is greater for negative tnan for positive 

 electrification. 





