1896.] 



On the Diurnal Periodicity of Earthquakes. 



305 



tion, therefore, between fertility and any mental or physical charac- 

 teristic must work a progressive change. 



We know that there are very considerable race and class differences 

 in the matter of fertility. It is very difficult to understand how these 

 could have arisen by the action of natural selection combined with 

 heredity, unless either (1) fertility be inherited, or (2) fertility and 

 some inherited mental or physical characteristic be correlated. But 

 either (1) or (2) involves reproductive selection. We have seen that 

 there is evidence of correlation between the stature of women and 

 their fertility. There is also evidence of a correlation between fertility 

 and class. Taking Copenhagen, for which alone we have satisfactory 

 class-fertility statistics, it is possible to show : 



(i) That the gross fertility of the artisan is more than the gross 



fertility of the professional classes. 



(ii) That the net fertility of the artisan is less than the net fertility 



of the professional classes. 



Thus natural selection, at first sight, checks reproductive selection, 

 greater fertility connoting a greater death-rate; but we find: 



(iii) That the marriage-rate of the artisan is so much higher than 



the marriage-rate of the professional classes, that the per- 

 centage fertility of the former considerably exceeds that of 

 the latter. 



Thus, while a selective death-rate checks reproductive selection as 

 between class and class, a selective marriage-rate again places repro- 

 ductive selection at an advantage as compared with natural selection ; 

 the population would accordingly appear to be ultimately, and in the 

 long run, reproducing itself from the artisan classes. 



I hope, later, to publish the analysis, curves, and statistics on which 

 these conclusions are based; at present I only wish to draw attention 

 to the general result : that reproductive selection — at any rate in 

 civilised man — seems a factor of evolution equipotent to natural 

 selection, if, indeed, it be not prepotent. 



II. " On the Diurnal Periodicity of Earthquakes." By Charles 

 Davison, M.A., F.G.S., Mathematical Master at King 

 Edward's High School, Birmingham. Communicated by 

 Professor Poyntino, F.R.S. Received February 15, 1896. 



(Abstract.) 



Reference is made to the previous work of De Montessus and 

 Omori, the former endeavouring to show that the diurnal periodicity 

 of earthquakes is apparent rather than real, and the latter pointing 



