Mr Campbell, The study of discontinuous phenomena. 131 



between theory and experiment of about 10°/^, in place of the 

 1 °/^ at which w^e have aimed. 



The best series of their results shows such an agreement 

 as might have been anticipated, but in other series the value 

 of A^ for large values of N was too large compared with that 

 for the small values. In the first series an aperiodic electrometer 

 was used, in the second a periodic instrument. It is not obvious 

 from the theory that has been given why this distinction should 

 be found between different experimental arrangements: for the 

 only difference made in equation (21) is that a and /3 are complex 

 with a periodic needle and real when the needle is aperiodic. 

 But Meyer and Regener's method of observing the fluctuations 

 is open to exception: they took a reading of 6' t orAy when the 

 needle reversed its motion at a peak in the fluctuation curve. 

 Now there is no reason that I can see for choosing the peaks for 

 observation in preference to any other points on the curve: the 

 effect of the various particles emitted is integrated by the instru- 

 ments at the peaks in a manner no less complex than when the 

 needle is moving constantly in the same direction. The only 

 justification for choosing the peaks is that they are easy to observe 

 (since the needle is at rest) and that they are points chosen at 

 random. Now it seems likely that there might be a tendency to 

 overlook peaks in the curve near the zero position of the needle, 

 when the total range of the fluctuation is small, and to observe 

 all the peaks which are more distant from the zero position. 

 This tendency would be the more marked, the gi^eater the range 

 of the fluctuations and the swifter the motion of the needle. For 

 the latter reason it would be more marked with a periodic instru- 

 ment than with an aperiodic, and for the former reason it would 

 be more marked when the total current was large. Accordingly 

 we might expect to find that, in the case of the periodic needle, 

 the observed values of A^ would be too large in the case of large 

 values of iV", relatively to those values for smaller values of N. This 

 differentiation is what is shown in Meyer and Regener's tables. 



On the whole, Meyer and Regener's attempt to prove the form 



of the relation between A^ and -^ seems to have been fairly 



satisfactory: but criticism can be directed against their attempt 



to deduce from A^ an absolute value for -^. In the first place, 



they seem to neglect altogether the effect of the constant of the 

 Bronson resistance and practically write 



A- = ^.a. 



