304 Danysz and Duane — Electric Charges of a- and $-Rays. 



minium equivalent in thickness to the walls of the radium 

 standard tube. The figures in columns 3 and 9 represent the 

 quantities of emanation in the spheres at the time of the 

 experiments (columns 1 and 7), and were calculated by means 

 of the law of decay of the emanation, using the constant 

 X= -0075 (hour -1 ). The quantities of emanation are expressed 

 in curies, the curie being the amount of emanation in equili- 

 brium with one gram of radium. 



Columns 4 and 10 contain the observed charges in electro- 

 static units received per second by the box E, with a magnetic 

 field of 8000 gauss and the cylinder B put to eartli ; and 

 columns 5 and 11 contain the values of these charges divided 

 by the corresponding quantities of emanation, that is, the 

 charges per second due to the a-rays from one curie of 

 emanation. 



That all the a-rays projected vertically upward emerge 

 from the glass sphere in these experiments may be inferred as 

 follows : columns 2 and 8 contain the thicknesses of the sheets 

 of aluminium that covered the hole C, and it appears that a 

 sheet -004: mrn thick did not diminish the magnitude of the 

 current per curie of emanation. All the a-particles, therefore, 

 must have left the surface of the glass with at least a certain 

 minimum velocity. The magnitude of this minimum velocity 

 may be estimated from the fact that no diminution in the 

 charge measured occurred on increasing the magnetic field up 

 to 8000 gauss. We have seen that, if rays are not stopped 

 by the field the radii of their paths must be at least 10 cm . 

 Hence, for the a-rays from the sphere 



mv . 

 Rr =: > 80000 



e 



or since, = 5xl0 3 approximately, 



„ cm. 

 v > 4 X 10' 



sec. 



The velocity of the a-particle when projected from the emana- 

 tion is 17 X 10 8 , and therefore all the a-particles emerging from 

 the sphere must have had velocities greater than about a quarter 

 of this. It follows that all the a-particles projected upward 

 must have passed through the glass wall of the sphere, for, if 

 a part of this wall had stopped a-particles neighboring portions 

 would have just let them through, and these would have had 

 small velocities.* 



* A diminution of the maximum current due to increasing the field up 

 to 8000 gauss was observed in the preliminary experiment mentioned above. 



