Radioactivity and Ionization of the Atmosphere. 721 



than the current of air, they will all reach the gauze B and 

 for a given current of air the current observed with the 

 electrometer will be unaltered when the strength of the 

 electric field is increased. Fig. 7. 



fc&Tfy 



It was experimentally observed that even with a small 

 electric field, there was some current to the gauze B. This 

 amount increased with the voltage to a practical maximum. 

 The experimental results are shown graphically in fig. 8 (p. 722) 

 for velocities of the current of air of 100, 205, and 250 cms. 

 per sec. respectively, when the gauze C was charged positively. 

 It will be seen from the curves that, for a velocity of 250 

 cms. per sec, the maximum current is reached with a P.D. 

 of about 350 volts. Since the gauzes were 2 cms. apart, the 

 velocity K of the positive ions for a potential gradient of 

 1 volt per cm. is given by 



*=v = 



hi 2 x 250 



350 



= 1*4 cms. per sec. 



where u is velocity of current of air and V the smallest P.D. 

 for which the maximum current is reached. The other two 

 curves also give a value of the positive ion of about 1*4 cms. 

 per sec. It was not found possible to obtain more than an 

 approximate result for the velocity of the ions, on account of 

 the variation in the conductivity of the air drawn through in 

 the course of a series of observations. The curves shown in 

 fig. 8 were obtained on special days when the variation of the 

 conductivity was small. 



Phil. Mag. S. 6. Vol. 4. No. 24. Dec. 1 ( J02. 3 B 



