Observations at the Poles of the Electric Air. 



967 



Finally, careful readings were taken with a hole of 



1*5 mm. diameter, selecting only the rare occasions on 



which the arc was really central. In every such case a 



Curves V. 



relatively large positive pressure was recorded. This result 

 was confirmed by a few readings taken with a smaller hoie 

 1*1 mm. in diameter. The order of magnitude of the effect 

 is given by the results shown in Table II., though the spot 

 rarely remained central long enough to ensure that the 

 gauge had filled up to the full pressure at the mouth of 

 the hole : — 



