216 LIGHT, VEGETATION AND CHLOROPHYLL 



the wide- spread use of contraceptives and a spate of pessimistic 

 literature which it is difficult to ignore. 



Nevertheless, Malthus's prophecies have not been fulfilled, 

 although the world has since trebled its population and that 

 of Europe has increased nearly four times — from an average 

 of 31 to 118 inhabitants per square mile. 



The problem is really very complex. In former times, the 

 peasant, firmly guiding his swing-plough drawn by a 

 robust pair of oxen, laboriously traced a furrow at the rate 

 of IJ miles per hour. He works ten or twenty times faster on 

 his tractor, but the tractor represents a certain number of 

 man-hours in the mine, the foundry and the factory, without 

 counting the work of the engineers and the preliminary 

 technical studies. Farmers now work better and more quickly, 

 but their number is decHning in every country. The United 

 States employ only one-fifth of their population in agriculture. 

 In 1870, half the population of France was engaged in farming, 

 compared with only one-third today, and we must expect to 

 see this proportion become smaller still. 



The economic pyramid is gradually rising and seems to be 

 dangerously multiplying its superstructures, while it rests on 

 a vertex which becomes relatively smaller every day. The 

 quantity of arable land is not inexhaustible and the most 

 probable estimates arrive at a total for the whole world of 

 some 6,000,000 square miles, i.e., 11 per cent of the land area. 

 Since there are 2,300,000,000 inhabitants. If acres of cultivated 

 land falls to each one and three men must live on 5 acres. 

 Atmospheric agents covetously degrade these Umited fields 

 and every year erosion carries away to the sea a mass of soil 

 rendered still more vulnerable by cultivation, while the land, 

 becoming exhausted as the years pass, demands more work 

 for a diminishing return. "How," exclaim innumerable Anglo- 

 Saxon writers, "can one avoid being alarmed to see the number 

 of human beings increasing and competing ever more 

 strenuously for the produce of these fields which are going to 

 ruin?" 



Although these views are shared by a growing section of 



