Electroscopic Measurements and their Prevention, 285 



Similar results were obtained for potentials of 400 and 

 350 volts. 



(3) A 2 always varies directly as A h decreasing as strength 

 increases for constant potential, and increasing with potential 

 for a constant strength of source. 



Subsidiary effects as well as the chief effect are shown 

 particularly with unweighted leaves where they are not 

 masked so much by the chief effect. The magnitude of any 

 leak for one fixed disposition varies slightly (1 to 3 per cent.) 

 according as (1) the leaf is charged so that it comes on to the 

 scale in the eyepiece within a short time, say 15 to 30 seconds ; 

 the leaf is charged up too much, and (2) it is brought almost 

 on to the scale by an extra source of radium which is then 

 removed ; or (3) it is allowed to come on to the scale under 

 the influence of the ionization which is being measured r 

 taking about 2 to 4 minutes to do so. Method (1) was used 

 generally and in making all measurements shown in fig. 1. 

 The effect of (2) is, as would be expected, to give a leak 

 slightly less than that obtained by (1). Thus a normal leak 

 obtained by charging up as in (2) would be slightly slower 

 than that made in the ordinary way. The effect of (3) is the 

 reverse of (2). In general the leaks obtained by successively 

 charging up to the same potential according to (1) lay on a 

 smooth curve extending from the normal to the maximum 



Fig-. 



r/<w£ //v Mwc/rss 



leak, such as shown in fig. 3. The influence of the methods 

 (2) and (3) was to give a point below the smooth curve and 

 above it respectively. After making such a measurement 



