PHYSICS — BARUS. 215 



results that it is possible to appreciably displace the ions during the period of 

 exhaustion, the reproduction being insufficiently rapid. 



(4) In a final investigation the endeavor was made to standardize the 

 coronas in relation to the number of fog-particles represented under given 

 circumstances of exhaustion, by aid of Thomson's electron. After a number 

 of trials, the first successful method consisted in making a closed aluminum 

 tube containing an even distribution of radium the core of a cylindrical con- 

 denser, leaded to an inch or more in thickness without. This core was sus- 

 pended axially from fine wire, leading to Dolezalek's electrometer for the 

 measurement of the small voltages and currents involved. The core in ques- 

 tion was then removed from the electrical condenser and put into the axis of 

 a dust-free fog-chamber, where the nucleation (ionization) was found from 

 the constants of the coronas obtained upon exhaustion, or vice versa. 



Using the method which depends essentially on the velocity of the ions in 

 the unit electric field and his earlier values of the constants of coronas, Dr. 

 Barus made a few rough tests of the charge of the electron, which gave very 

 reasonable values. Experiments made under different conditions showed, for 

 instance, e X io^° = 3.7, 4.3, 3.8, 3.4 electrostatic units of charge in the dif- 

 ferent cases, whence it follows that both positive and negative ions must have 

 been captured. 



There was, however, an inherent difficulty of great importance, the nature 

 of which has already been referred to. The ionization differs in different 

 parts of the fog-chamber and the extreme ratios may exceed 2 t© i. It does 

 not follow, therefore, that the mean ionization observed in the fog-chamber is 

 the same as that obtaining within the heavy leaded electrical condenser. To 

 secure this identity the fog-chamber itself must be the condenser. 



The method was, therefore, varied by using the cylindrical fog-chamber 

 (glass wet within, put to earth), with its axial core of charged aluminum 

 tube, both as an electrical condenser for the measurement of current and as a 

 fog-chamber for the measurement of ionization. The end of the aluminum 

 tube within the fog-chamber is hermetically sealed ; the other is open without 

 for the introduction of the sealed tubelets containing radium. By properly 

 adjusting these along the axis, an approximately uniform ionization within 

 the fog-chamber is obtainable. The trials made seemed promising enough to 

 make it worth while to repeat the determination of e by Thomson's method, 

 using, however, the mercury lamp as a source of light and a purely optical 

 method for the measurement of the nucleation, as suggested above. 



(5) The correlative method of determining e in terms of the decay constant 

 b = 1.1 X io~^ of the ionization has also been tried. If N be the number of 

 ions in the fog-chamber due to the radium in the aluminum tube when the 

 latter is not charged and n the number when it is charged, the con- ant e may 

 be written e=C V / [b(N^ — n^)v'], where C is the capacity and :■ the vol- 

 ume of the cylindrical condenser-fog-chamber and V the (constant) fall of 



