Rays and Product of Uranium X. 



343 



the new minimum value of 35,000 years instead of the old 

 value of 18,000 years for the period, it follows that the 

 maximum growth of a-rays to be expected from the uranium X 

 preparations corresponds to only 5 divisions a minute, and 

 the detection of this would have been doubtful. Whereas, if, 

 as is not improbable, the real period is much longer than this, 

 the theoretical growth of a-rays becomes certainly too small 

 to be detectable. 



In all the preparations the /3-rays have decayed normally, 

 so far as can be seen, and in the older preparations are now 

 scarcely detectable. For all the preparations, measurements 

 of the a-radiation by the method and apparatus previously 

 described can now be done without excitino- the mao-net, 

 and practically the same results are now obtained for the 

 a-radiation, whether the magnet is excited or not. This 

 shows that the method is trustworthy, and that the small 

 proportion of /3-rays escaping deviation did not interfere with 

 the initial measurements of: the feeble a-radiation, when the 

 preparations were intensely active. This proportion can now 

 be accurately calculated from the known constant of decay, 

 0-0282 (day)" 1 (Soddy and Russell, Phil. Mag. 1910, xix. 

 p. 847). About y-l-Q part of the /3-rays escape deviation, 

 and therefore it would appear must possess a value for Up 

 above 8640. 



Most of the preparations have now decaved sufficiently far 

 for the a-radiation to be accurately measured in an ordinary 

 electroscope. There certainly has been no increase in the 

 a-rays. Indeed, the results rather indicate a very slow decay; 

 but more time must elapse before this can be verified. 



With regard to the a-ray measurements in hydrogen with 

 the magnet, the results with all the preparations show practical 

 constancy from the start, and the small variations are doubtless 

 due to unavoidable changes in the atmospheric conditions at 

 the time of measurement. The following table refers to the 

 observations with the preparation of the fourth separation. 

 The first 10 observations previously given (ibid. p. 863) varied 

 between 37*1 and 40*5, with 38*9 as the mean. 



1 



Time (clays) ... 0-33 



1 (Mean of 10) 



61 



75 



198 



284 



*-rays 389 



39-9 



39-5 



36-9 



38 





The preparations of the second and third series have 

 behaved quite similarly. The oldest of these was prepared 



