378 



Dr. G. A. Blanc on the Radioactive Matter 



whole number frequencies, those for the curve being found 

 by mechanical integration. 



Percentages. 



Frequenc 



es. 



Percentages. 



\ 

 Frequencies. 



- 

 Hypergeo- 

 metrical. 



Curve. 



Hypergeo- 

 metrical. 



Curve, i 



Less than - 5 



133 



134 



6 



17 



18 



1 



258 



259 



7 



6 



7 i 



2 



261 



257 



8 



2 





3 



181 



179 



9 











•1 

 5 



98 

 44 



98 

 45 



10 











Sum 



1000 



1000 1 





J 



Conclusions. — The method often adopted for measuring 

 the expectancy of a future sample from past experience is in 

 certain respects defective, when (i.) the size of the future 

 sample is at all comparable with the past experience, (ii.) the 

 characteristic expected occurred only in a small percentage 

 of cases in the first experience. In such cases the mean and 

 probable error of the expectancy can be easily found, and 

 depends upon the relative sizes of the past experience and of 

 the future sample. The frequency of future samples is given 

 by a certain hypergeometrical series, which is not at all closely 

 represented by the Gaussian curve except when the past expe- 

 rience is very large as compared with the proposed sample, and 

 further the characteristic expected does not occur in either a 

 very large or very small percentage of the population. 



/ 



XXVIII. On the Radioactive Matter in the Earth and the 

 Atmosphere. By G. A. Blanc, Ph.D. {Rome) *, 



IN a paper published in the Philosophical Magazine 

 (September, 1906), A. S. Eve has given the very 

 interesting results of the investigations made by him on the 

 radioactive matter contained in the soil and atmosphere, 

 concluding that the presence of radium in the earth and 

 radium emanation (with its successive transformation pro- 

 ducts) in the atmosphere are the principal cause of the 

 ionization which is observed in the open air and inside 

 buildings. 



Eve comes to the conclusion that a proportion of 1*8 X 3 0~ u 

 gr. of radium bromide per c.cm. uniformly distributed in the 



* Communicated bv Lord Kelvin. 



