Duane — Emission of Electricity. 3 



4. With the tube B connected to earth the electrometer 

 always indicated a current flowing toward the electrode A, or, 

 what would produce the same deflection, a discharge of negative 

 electricity away from it. The current continued until the elec- 

 trode became charged to a positive potential in the neighbor- 

 hood of one volt, at which potential the discharge was apparently 

 compensated by a flow in the opposite direction. A Yolta 

 electromotive force always acts between the tube B and the 

 electrode A, even if they are of the same material. This 

 electromotive force could be determined by reading the per- 

 manent deflection of the electrometer before exhaustion, when 

 the space between A and B contained air. Usually the deflec- 

 tion indicated an electromotive force of about y^th of a volt, 

 and always one in such a direction as to oppose the current in 

 the vacuum. Hence the observed discharge of electricity can- 

 not be due to the Yolta electromotive force. The electromotive 

 force decreases with the time, but judging from some experi- 

 ments I have made, it is not directly due (at least for the most 

 part) to the deposit of radium A, B and C on the electrode. I 

 have tried to obtain evidence for such a Yolta effect, but have 

 not succeeded. 



5. The Yolta electromotive force, however, alters the mag- 

 nitude of the discharge, and for this reason in taking readings 

 for the decay curves of the induced activity I adopted the 

 usual method of charging the tube B successively to equal and 

 opposite potentials. If B is charged to a positive potential of 

 1*5 volts or more, a current flows toward the electrode, and 

 reversing the sign of the potential reverses the direction of the 

 current. The current toward the electrode, however, is con- 

 siderably larger than that away from it, the excess being due 

 to the discharge of negative electricity from it. 



6. Tables I and II contain several series of readings. The 

 amounts of radium emanation used to make the electrode 

 radio-active were those produced from 3 or 4 mg of KaBr 2 

 in one to five days. No attempt was made to collect all 

 the induced activity on the electrode, and probably a large 

 part of it settled on the tweezers that held the electrode in the 

 emanation. Table I contains the results of experiments with 

 an iron electrode and tube. In the first column the time after 

 the electrode was removed from the emanation is tabulated, 

 and in the second and third the currents to and from the elec- 

 trode produced by potentials of ±2*2 volts applied to the 

 tube. First the current toward the electrode (called hereafter 

 the positive current) was measured, then two minutes later the 

 negative current and so on alternately. The corresponding 

 columns of Table II contain similar results for a brass elec- 

 trode and tube. 



