Duane — Emission of Electricity. 13 



changing into C discharges as much electricity as does radium 

 C when changing into D. 



(b) A magnetic field parallel to the active surface stops part 

 of the emission of electricity ; and an electric field normal to 

 the surface also alters the rate of discharge, the magnitude of 

 the electric and magnetic effects being about what would be 

 expected if the charge was carried by electrons, a considerable 

 portion of which had component velocities normal to the active 



surface in the neighborhood of, or less than, 4xl0 6 



cm 



sec 



(c) The total quantity of negative electricity emitted per 

 second by an active brass surface is at least as large as the 



th part, and probablv larger than the th part of the 



9000 r 9 f ,5 3600 F 



ionization current that can be obtained from the activity, if the 

 a rays from radium C are completely absorbed in the air pro- 

 ducing their maximum ionization ; i. e., the number of ions 

 produced by the a rays in air is less than 9,000 times, and probably 

 less than 3,600 times the number of /3-particles expelled from 

 the wire during the same time. Assuming that each a particle 

 from radium C can produce 180,000 ions, this means that for 

 every a particle expelled from radium C, at least 20 and proba- 

 bly more than 50 electrons are emitted from an active brass 

 surface. 



(cl) The number of ions produced by radium B in the air 

 at atmospheric pressure close to (i. e. within \ a mm. of) the 

 active surface is comparable with the number of ions produced 

 in the same space by radium C. 



Radium Laboratory, University of Paris, 1908. 



