11 



amount of ionization in the air drawn off was at first very- 

 large, but decreased at first rapidly and then more slowly 

 as the shot continued to fall, asymptoting, apparently, to a 

 definite minimum value. A typical set of readings exhibit- 

 ing this 'fatigue" effect is as follows : —7*0, 62, 52, 4*9, 4*3, 

 4'1, 40, 3'9, 3'7, 3 - 5. For this reason it was found impos- 

 sible to compare satisfactorily the magnitude of the effect 

 ■with targets of different metal and also with shot of different 



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diameters. When targets of glass or ebonite were employed 

 the above effect was insignificant, a steady reading being 

 obtained from the outset. Thus with a glass target the suc- 

 cessive readings 1"9, 2'2, 2'2, 2'1 were obtained; with an 

 ebonite one 3*1, 3'0, 3 '05. 



Ionization is likewise found to occur whatever substance 

 be allowed to fall on the target, e.g., with sugar, salt, caustic 

 soda, etc., the effect with sugar being larger than for any other 

 substance examined. 



