10 Duane — Emission of Electricity. 



known formula for the radius It of the cylinder along the sur- 

 face of which a /3-particle moves in a magnetic field iZ, 



when u is the component velocity normal to the field, m 

 the mass and e the charge of the particle. If any of the 

 particles projected from one surface have velocities so small 

 that R is less than \ the distance to the other surfaces, 0'22 mm 

 they will not reach the other surface. Further, some par- 

 ticles for which R is greater than this will be cut off also, 



by the field. Assuming that the ratio — for the carriers of 



electricity is that of the electrons, namely 1*87 XlO 7 , the 

 velocity for which i2=0'022 cm is 



m 



It follows that a considerable number of the electrons must 

 have velocities near or less than 4 XlO 8 . 



17. The effect of increasing the electromotive force applied 

 to the tube B was also studied, measurements being taken 

 during a series alternately with 1*5 volts and voltages rang- 

 ing up to 80 volts. It appears that both the positive and neg- 

 ative currents a,re considerably increased by increasing the 

 electric field, and that, up to 40 volts at least, their algebraic 

 sum is decreased. These results can be explained on the 

 assumption that the currents are carried by the /3-particles 

 shot off from the surfaces. An electric field between the con- 

 ductors stops some of them. To calculate the velocity that -40 

 volts would stop we have 



|mw 2 =40Xl0 8 e 

 or w=3-8X10 8 



It follows, as before, that a considerable number of the elec- 

 trons must be projected with component velocities to the sur- 

 faces in the neighborhood or less than 4X10 8 . 



18. Combining the electric and magnetic effects we might 



calculate values for both — and u, but owing to the complexity 



m 



of the rays, and the difficulty of estimating just how many 



particles have velocities under a given limit, such estimates 



would not be worth much. The experiments show, however, 



that the order of magnitude of the effects are such as would 



be produced, if the currents were carried by /3-particles, a 



considerable number of which had velocities normal to the 



surfaces in the neighborhood of 4 XlO 8 or less. 



