produced by Beta Rays. 787 



have no connexion with those by which Curie and Sagnac 

 proved that metals under the influence of Rontgen rays 

 emit negatively charged rays of considerable penetrating- 

 power. The form of the curves obtained here is determined 

 wholly by rays which have a velocity less than 40 volts. 

 The secondary ft rays have a velocity of several thousand 

 volts, and they will pass from one electrode to the other 

 practically uninfluenced by the small P.D/s employed. 

 Their only effect will be to produce a current independent 

 of the P.D.'s if the number of secondary rays emitted from 

 the two electrodes is not the same. The value of i+yr-Ly 

 is, of course, independent of such a current. 



7. Two results obtained incidentally may be mentioned. 

 The first is not of any great importance. It has often been 

 announced that the number of § rays given off by a source 

 of a rays is greater than that given off by any substance 

 struck by the rays from that source. The experiments in 

 which the source of a rays was the active deposit of thorium 

 on one of the electrodes show that this announcement is 

 erroneous. It has usually been made as a result of measure- 

 ments with polonium, and the apparently greater emission 

 from that substance is to be attributed to the entanglement 

 of the £ rays liberated in the soot-like deposit in which the 

 polonium is contained (see the investigations on soot-covered 

 electrodes in Phil. Mag. Jan. 1912, p. 16, &c). 



8. The second is perhaps more important. When both 

 electrodes were covered with paper the amount of & rays pro- 

 duced from them was certainly less than 1 per cent, of that 

 produced from the electrodes when covered with gold ; but 

 when one electrode was covered with paper and the other with 

 gold, the amount of g rays produced at both electrodes was 

 approximately the same. It has been explained in the former 

 papers why it is difficult to determine with any accuracy the 

 respective contributions of the two electrodes to the current 

 when they are covered with different materials. There was 

 no evidence of any difference between the contributions of 

 the gold and the paper electrodes, but they may have differed 

 by as much as 30 per cent. Since the electrodes were so 

 arranged that very nearly all the secondary ft rays excited 

 from one electrode would fall on the other, these observations 

 would seem to show that the number of $ rays excited by a 

 given number of ft rays is (like the number of g rays excited 

 by a given number of a rays) almost independent of the 

 material on which the rays fall ; and they show also that the 

 emission of § rays is determined by the number of ft rays 

 acting,' and not by the number of Rontgen rays. N o § rays 



