Relative Density of Population in Repre sentative Countries.—We of the United States can scarcely realize how much greater is the density of population in certain other coun tries than that of our own. We have in continental United States, exclusive of Alaska, an average of 36 persons per square mile, while Germany has 325 per square mile, Italy 332, Japan 392, Netherlands 499 and England an average of 624 per square mile, or 17 times as much as our own. If all the people of the en tire world were set down in continental United States, exclusive of Alaska, our average density of population per square mile would be less than that of England to-day. Yet England is looked upon as one of the most prosperous countries of the world and feeds her densepop ulation in large part with food brought from other countries, often from the opposite side of the globe, and paying for the same with the product of her factories.
The Drift to Industrial Centres.—With this change in the habits of life among the people of the world, the exchange of food of the agri cultural areas for the manufactures of other areas, the density of population in the manufac turing areas has gone on increasing without the danger of starvation or food shortage which existed a century ago when cheap transporta tion of food across the ocean was impossible. In England, for example, the share of the popu lation living in cities of 10,000 or more was in 1800 but 21 per cent and 66 per cent in 1900. The British census of 1851 classed 49 per cent of the population as °rural)) and in 1911 only 22 per cent was classed as The population of the 12 great cities of England was in 1820 2,000,000 and in 1919 is 9,000,000. In Scotland in 1800 only 17 per cent of the people lived in cities of 10,000 or upward; now it is over 50 per cent. In Prussia in 1800 only 7 per cent of the people lived in cities of 10,000 or more; in 1890 it was 30 per cent and at the beginning of the war ap proximately 40 per cent. These changes are the result of a transfer of labor in the older coun tries from agriculture to manufacturing and reliance upon younger countries for food and manufacturing materiaL This habit of accumulation of population in dense masses and of drawing food from other areas better able to produce material of this character is exemplified in a striking degree in the United States which has recently become a great manufacturing country. The share of our own population living in cities of more than 10,000 was in 1800 only 4 per cent ; in 1890 it was 28 per cent, while the share of the population living in cities of 2 500 or more in 1910 was 46 per cent and at tfie present time is approxi mately 50 per cent. Thus it may be said that even in this comparatively new country, with its large agricultural powers, approximately one half of our population now live in cities or and draw their food and manufacturing material from other areas, some of them on the other side of the globe. While the United States is still the world's greatest producer of both food and manufacturing material, it now brings from other countries, mostly across the ocean, about $2,500,000,000 worth of food and manufacturing material Annually, and these two groups of material actually form 85 per cent of the merchandise imported into this country, much of it traveling half-way round the world before entering our ports. Great Britain is another example of the reliance upon other parts of the world for food, since with a pop ulation less than half our own she brings in normal years nearly $3,000,000,000 worthof merchandise, chiefly food and manufacturing material from other countries, much of it across the ocean.
Will the Recent Growth of Population Continue?— Now a word as to the future. The population of the world has doubled in the past century. Will it double again in the next 100 years? Probably not. The rate of growth has perceptibly slowed down in the past quarter century and is now at the rate which suggests a net increase of little more than 1,000,000,000 in world population during the next century, giving a grand total of about 3,000,000,000 as the world's entire population a century hence.
Can the world sustain a population of 3,000, 000,000 as against 1,700,000,000 at the present time? Undoubtedly. The developments of science and industry will bring under the control of man vast areas now contributing practically nothing to his support. The great tropical and subtropical belt which stretches round the world between the 30th parallels of north and south latitude has about one-half of the land area of the globe, but now supplies but one sixth of the products entering international commerce, despite the fact that its producing power per acre or square mile is double or treble that of the like area in the temperate zone. With the lessons of the war, man has learned to substitute the internal combustion engine for the horse which could not perform a satisfactory service in the tropics, and with this new instrument of production and trans portation he will now, after long years of wait ing, be able to conquer the tropics and multiply the production of the food and manufacturing materials which they can so easily turn out and for which the other sections of the world are clamoring. The producing power of the older and longer cultivated lands of the world is largely dependent upon the soil foods sup plied, and with the lessons of the war, man has learned to reach out into the air and obtain unlimited quantities of that most im portant of soil foods, nitrate, utilizing' for that work the power of the waterfalls which has been going to waste in the past. The great deserts of the world now producing noth ing have shown that they only need the appli cation of water to render them more productive per acre or square mile than those of the areas now under cultivation, and man is grad ually learning methods of bringing to them the necessary moisture from beneath the surface or from distant water courses, and at the same time has learned through the application of dry farming° to obtain enormous auantities of food from areas formerly considered of little value as food producers. The substitution of the internal combustion engine, utilizing gasoline, kerosene, heavy oils or alcohol, will take the place of the horse and thus release enormous areas of land hitherto devoted to produc ing food for that animal whose services will be no longer required. The scien tists of the world are showing us every day the feasibility of utilizing for food purposes untold quantities of natural products which have been permitted to go to waste in the past, while the world is also gradually coming to understand the importance of so conserving the products of nature as to render them far more valuable in the future than under the wasteful methods of the past.