734 FroiUms of Helium and Radium. [June 11, 1909 



or at least six times the rate of production found in the above 

 experiments. I am at a loss to explain the origin of such grave 

 discrepancies in the measured amount of the helium produced by 

 radium. On the other hand, Professor Rutherford, in his work 

 entitled " Radio-active Transformations," 1906, page 186, on the 

 theoretical assumption that the particle is an atom of helium carrying 

 twice the ionic charge, deduced from electrical measurements that the 

 number of particles expelled per year per gramme of radium would 

 reach 4 x 10'^ and as 1 c.cm. of a gas at standard temperature and 

 pressure contains 3'6 x 10'^ molecules, the volume of helium pro- 

 duced per year would amount to 0*11 c.cm., which is equivalent to 

 about • 3 c.mm. per day. 



It is interesting to note that a more recent calculation made by 

 Rutherford from theoretical considerations of radio-active data, gives 

 a result of • 45 c.mm. of helium per gramme of radium per day, as 

 compared with the earlier calculation of about 3. The agreement 

 between experiment and the theoretical prophecy of Rutherford is 

 remarkable considering the difficulties to be overcome in the observa- 

 tions ; substantiating as it does the accuracy of the theory of radio- 

 active changes which he has done so much to develop. 



If the helium in the atmosphere was produced chiefly from the 

 radium present in sea- water, Strutt's experiments demand 100 million 

 years for its accumulation. Joly's examination of samples of the 

 ocean beds from the ' Challenger ' Expedition revealed the presence 

 of considerable amounts of diffused radium, which would shorten this 

 period. Such conclusions are based on the estimation of very minute 

 quantities of radium, and it is just as likely that 50 million years 

 might suffice to account for all the helium present in theJatmosphere 

 as the 100 million year estimate given above. 



[J. D.] 



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