Danysz and Duane — Electric Charges of a- and ft- Rays. 299 



and may produce more secondary rays in the direction of their 

 own motion than in the reverse direction, or vice versa ; and 

 further, even when the two boxes are at the same potential 

 there may be a small electric field between them due to the 

 Volta electromotive forces. 



If the cylinder B is charged positively the negatively 

 charged secondary rays are pulled downward, thus producing 

 a positive current upward toward the box E, and when the 

 field is so strong that the current has reached its maximum 

 value all the secondary rays projected upward from the lower 

 sheet are stopped by the electric force. If the cylinder B is 

 charged negatively the secondary rays are pushed upward, thus 

 creating a negative current upward, and all the rays projected 

 downward from the upper sheet are stopped when this current 

 is saturated. 



The order of magnitude of the velocity of the secondary 

 rays, supposing them to be electrons, may be estimated from 

 the difference of potential required to stop them. If Y is this 

 difference of potential, and v, m, and e are the maximum 

 vertical velocity, mass and charge of the electrons 



— mv 2 = Ye 



2 — - 

 m 



s 





 For electrons = 1*77 X 10 7 , and taking for Y 40 volts 



= 4 X 10 9 e, m, u, we have 



v = 3-74 X 10 e ( 



sec. 



It must be borne in mind that those rays, to which the name 



cm 



/3-ray has been attached, have velocities greater than 10 10 » 



sec. 



and that a difference of potential of many thousands of volts 

 would be required to stop them. The a-rays could not be 

 stopped by any difference of potential obtainable. 



The general truth of the above manner of explaining 

 the currents is confirmed by measurements with a magnetic 

 field. On putting the cylinder B to earth and on increasing 

 the magnetic field from to 8000 gauss, one observes the 

 currents represented by curve 1 in figure 3. Up to about 60 

 gauss there is a sharp fall in the value of the current. That 

 this is due to the suppression of the secondary rays by the 

 magnetic field may be made clear by the following considera- 



