Radio-active Products of Short Life, 629 



a successive product o£ the group thorium G without any 

 assumption, whether it originates from only one o£ the com- 

 ponents or both. The analogy between the general modes 

 of the three emanations is undoubtedly very close. It 

 appears very probable that the group radium C in reality 

 corresponds to the group thorium C + D, and actinium C + D, 

 although the type and order of the transformations appear to 

 be different in each case. There are, however, still many 

 questions to be closely examined before any decisive con- 

 clusion can be reached. The analogy between the products 

 of the emanations has been discussed in some detail partly to 

 give reasons for the scheme of nomenclature adopted, and 

 partly to bring out the numerous points of similarity. 



University of Manchester, 

 August 1911. 



LIX. Radio -active Products of Short Life. 

 By H. G. J. Moseley, B.A., and K. Fajaxs, Ph.D.* 



THE ordinary methods by which the properties of radio- 

 active substances are investigated are not suited to 

 the study of products of short life. The shortest period 

 hitherto measured, that of actinium emanation, period 

 3' 9 seconds, was determined by a method of steady flow. 



The emanation supplied at a constant rate from an 

 actinium preparation was conveyed with a steady stream of 

 air through a tube. The period was deduced from obser- 

 vations of the concentration of the emanation at different 

 points along the tube. 



Evidence, which will be discussed later, pointed to the 

 existence of products of yet shorter life ; the steady flow 

 method was accordingly adapted to their investigation. 



By this method the periods were determined of two pro- 

 ducts, the one successive to actinium emanation, the other 

 to thorium emanation. The periods were found to be -0020 

 second and 14 second respectively. 



Throughout this paper the new nomenclature proposed by 

 Rutherford and Geiger f will be adopted. To avoid con- 

 fusion the period will be added in brackets whenever a 

 product is mentioned of which the name has been altered. 

 The two products just mentioned will therefore be called 

 Actinium A (*002 sec.) and Thorium A ('14: sec). 



The steady flow method can be used to investigate any 



* Communicated by Prof. E. Rutherford, F.R.S. 



f See preceding- paper. 



Phil. Mag. S. 6. Vol. 22. No. 130. Oct. 1911. 2 T 



