THE MIGRATION OF POPULATIONS 73 
that naturally occurs is, “ How quickly can the world 
advance to such densities as have been referred to, for 
her peoples?” and the second is, “In what regions 
will the situation first become one of challenging 
difficulty? 2” We may, therefore, perhaps at the risk 
of being tedious, refer again to the significance of the 
rates of growth. For the last one hundred years it 
may be taken as two-thirds of a per cent. per annum. 
Assuming the world-population for 1928 to be 1950 
millions, the four limits 5200, 7020, 9ooo and 
11,000 would be reached in only 1476, 1928, 230-2 
and 260-4 years respectively, if the rate continued 
constant; that is, before the following years of this 
era, viz., before the year 2076, or 2121, or 2I§8, 
or, finally, before 2188. These are but short periods 
in history; they are very roughly only about one- 
thirteenth, one-tenth, one-eighth, and one-seventh 
respectively of the present era of 1928 years. 
If the annual rate for the western world from 1906 
to 1911, viz., 116 per cent. per annum, were to hold 
continuously for the whole world, these limits would 
be reached in much less time, viz., in 85-0, 111-1, 
1326 and 150-0 years respectively. It does not 
materially alleviate the situation, either, to be told 
that the rates of increase will diminish as the limit, 
whatever it be, is approached, and that the ultimate 
figure will be very slowly reached. Long before 
that figure has been attained the population-difficulty 
will have become terribly acute, and it has to be 
borne in mind that, from time to time, the trouble 
about populations and their food-supplies is certain 
to be painfully accentuated by the inescapable vicissi- 
tudes of Nature. Man can cope with these to some 
extent, it is true, but, after all, only very inefficiently. 
He has learnt to modify the disaster coming upon 
him through a drought, but he cannot wholly escape 
appalling losses. Recently he has again been reminded