E— GEOGRAPHY 121 



are apparent local exceptions, often due to the developments of tourism ; 

 though this industry maintains only a small, and often only a seasonal, 

 local population, and it stimulates the exodus by increasing contacts with 

 the outer world. 



In some newer countries there is also a retreat of settlement from some 

 thinly peopled areas. In the same decade, 1921-31, Australia saw a 

 definite withdrawal of settlers from its inner areas of less than fifteen 

 inches of rain towards the more humid regions nearer the coasts. And 

 the still more recent exodus of ruined settlers from the semi-arid areas of 

 the American ' dust-bowl ' is more widely known. In these semi-arid 

 regions it seems that close settlement had been pushed beyond its safe 

 limits. The system of ' dry farming,' which had been widely introduced, 

 involves the destruction of the natural vegetation cover and the loosening 

 of the topsoil. Over-grazing has a similar effect because it compels the 

 cattle to pull up and devour the stems and roots of the grasses. When this 

 is followed by a more than usually dry season, accompanied by strong 

 winds, the fine topsoil is blown away, and with it most of the plant-food. 

 So both dry-farming and over-grazing are desert makers. 



Such local retreats from unattractive areas are nothing new in the history 

 of mankind. And it appears that there are more important general causes 

 for the present trends of migration towards populous regions and great 

 urban centres. Most of these seem to be results of the application of 

 scientific knowledge to the work of the world. So that these great 

 population shifts are essentially a result, and among the most important 

 social results, of the developments of applied science. 



First among these general causes I would put the diminution in the 

 proportion of the world's workers who must be devoted to satisfying the 

 primary needs of food, clothing and shelter, and to making the tools 

 wherewith to do this. At the beginning of the Industrial Age more than 

 half of all the working population of every country was directly engaged 

 in the production of food, and of vegetable and animal raw materials, for 

 most of their working life. Their manual power was supplemented by 

 the labour of domestic animals and, to a small extent in some favoured 

 regions, by clumsy wind- and/or water-mills. Now these industries have 

 received a new equipment of immensely more efficient tools (compare the 

 combined harvester with the sickle and the flail), of better and more pro- 

 ductive seeds and animals, of more eff^ective methods such as the rotation 

 of crops, of better fertilisers, and of more efficient workers. As a result, 

 their productive capacity has increased so that they can provide a much 

 higher standard of material living for a greatly increased population. At 

 the same time the proportion of the workers needed has fallen. It is now 

 only some twenty per cent, of the total ; and it seems likely to fall still 

 further. 



Similar changes have taken place in other primary industries. Such 

 changes as the substitution of the steam-shovel and the excavator for the 

 navvy's pick and spade, of concrete produced almost wholly by machines 

 for the laboriously shaped stones of the quarryman and the mason, of the 

 spindle for the spinning-wheel, have enormously reduced the amount of 

 direct manual labour needed in many industries. 



