2i 4 THE POPULAR SCIENCE MONTHLY 



Beyond the plowed fields of the present, the arid and wet lands and the 

 superfluous forests, are no inconsiderable reserves of food from lands 

 deemed useless. We may consider potential gardens along more than 

 two hundred thousand miles of railway, the fruit that might grow by 

 millions of miles of highway, the steep and immature slopes that are 

 more capable of terracing than those of Capri or Amalfi, or ancient 

 Palestine, and finally those rugged areas of glacial hillside or mountain 

 slope, where nut-bearing trees might produce no inconsiderable amount 

 of highly nutritious food. The possible production of food substances 

 in the laboratory is at present so far from the geographer's domain that 

 it would be profitless to dwell upon it. 



It is plain that the whole circle of conservation problems applies 

 here, not only by directly increasing food, as in irrigation, but in 

 cheapening the cost of transportation, in saving land by forest conserva- 

 tion and in utilizing power of every kind to the full, thus releasing time 

 and energy for the free use of opportunity and the complete employment 

 of all our resources. Thus a well ordered civilization would sustain 

 the greatest number at good standards, as a well-managed household 

 may maintain a large family on a lesser sum than is required by a 

 neighboring small household. 



Population capacity would afford a less baffling inquiry if food alone 

 were needed. Mere questions of mouths, bushels and pounds might 

 involve simple ratios, easily determined,' but we must at once include 

 clothing, of vegetable fibers, animal fibers, furs and skins, nearly all 

 requiring land for their production. Man must have shelter and a 

 long catalogue of objects of domestic utility, for the household and for 

 the tillage of the soil. These things may become chiefly derivable from 

 subterranean sources with the single exception of a minimum demand 

 on the forest. Many rocks and mineral substances would far outrun 

 any possible use of them, but it seems certain that we could not for 

 many generations supply iron for as many millions as we can feed. It 

 may be doubtful whether our ultimate expansion will receive its first 

 effective check above or below the surface of the earth. 



"We must include also a wide range of objects of public utility, such 

 as roads and all appliances of transportation and manufacture, and 

 public structures for education, worship, government, health and 

 charity, adding instruments of knowledge and pleasure such as books, 

 music, ornaments and all works of art. 



Almost as fundamental as food is the requirement of power. Here, 

 however, the supply seems ample and permament. Long before the 

 stores of buried fuel are exhausted, other natural forces, particularly 

 that of moving water, will meet the needs of any population which we 

 can feed. The maximum of population therefore for the whole world 

 hinges upon the supply of material substances derived from the atmos- 

 phere, the water, the soil and the rocks. 



