Electricity through rarefied Gases. 787 



the bulb reduced to a certain value. The potential of the 

 anode is then gradually raised by means of the spark-gap, 

 and the current carried by the positive ions from the strip 



Fig. 1. 



is measured. This current was usually of! the order of 

 10" 6 amp. When the potential of the anode becomes 

 sufficiently high (corresponding to a spark-length ofi say, 



