Production and Origin of Radium. 733 



surface ; the amount of emanation in the atmosphere ; the 

 resulting active deposit ; the penetrating radiation due to all 

 these ; the ionization in the atmosphere : all are of the correct 

 order of magnitude, so that they may be correlated. 



Residt.— The emanation in the atmosphere is absorbed 

 by coconut-charcoal : its presence can be proved and its 

 magnitude determined. 



Four measurements have been made at Montreal, and the 

 results are given in terms of the amount of radium required 

 to maintain the supply per cubic metre constant. The 

 smallest value obtained was 24 x 10 -12 , the largest 127 X 10~ 12 . 

 The probable average value is 80xl0 -12 . The amount of 

 emanation is of the correct order to account for the active 

 deposits of radium C, which may be collected on negatively- 

 charged wires from the atmosphere. 



Now that Professor Rutherford has left McGill University, 

 I wish to state my indebtedness to him. If my papers have 

 had any merit, it may be attributed, without exaggeration, 

 to his influence or inspiration, and for these I am grateful. 



McGill University, Montreal, 

 August 1907. 



LXXIII. The Production and Origin of Radium. By E. 

 Rutherford, F.R.S., Professor of Physics, University of 

 Manchester* '. 



§ 1. rTlHE present point of view of regarding radium as a 

 JL substance which is undergoing slow transforma- 

 tion was first put forward definitely by Rutherford and 

 Soddy in the paper entitled "Radioactive Change" (Phil. 

 Mag. May 1903, p. 590) in the following terms : — " In the 

 case of radium, however, the same amount (viz. about 

 1 milligram) must be changing per gram per year. The 

 ' life ' of the radium cannot in consequence be more than a 

 few thousand years on this minimum estimate, based on the 

 assumption that each particle produces one ray at each 

 change. ... So that it appears certain that the radium present 

 in a mineral has not been in existence as long as the mineral 

 itself, but is being continuously produced by radioactive 

 change. J ' 



On this theory, the parent substance which produces radium 

 must always be present in minerals containing radium. 

 Uranium from the first appeared to be the most probable 



* Communicated by the Author, having been read before the British 

 Association, Leicester, August 1907. Previous accounts of the results 

 were given in letters to ' Nature,' Jan. 17 and June 6, 1907. 



