The topic will be discussed under the heads which have been employed previously in similar discussions. The advances have been achieved either by a gain in the power of man to control nature and natural forces (technical progress); or by the more efficient cooperation of men in business (industrial and commercial organization), or in politics (political organization, domestic and foreign policy). =321. Prime importance of technical factors, especially the use of coal.=—Hard as it is to disentangle these different factors, all of which have contributed much to the recent progress of the world, there need still be no question which has been of the leading importance during the nineteenth century. This century has been the great era of material invention, of scientific discovery, and of the increase in power of man over nature. Technical progress, therefore, is the first subject to be studied. Again, there need be no question as to which feature of technical progress holds first place. Electrical appliances? Machinery? The steam-engine? Applied chemistry? All those things, with the vast benefits which they confer on humanity, rest now on practically one basis: coal. Vegetable matter of past geological ages, that has become fossilized, has undergone mysterious chemical changes and has shrunk to one tenth of its former bulk, furnishes now, after hundreds or thousands of centuries, the means by which we maintain and develop our material civilization and our great commerce. =322. Power in coal.=—Coal offers men what all men seek, power. There is “spring” enough in it, when properly applied, to raise a million times its own weight a foot high. A man who sends a horse and cart to fetch a ton of coal, occupying four hours on the way, secures a power in the coal theoretically 2,800 times that expended in bringing it; and can probably get from it an amount of useful force exceeding by 100 times or more that of the horse employed in carting. A few decades ago (1865), when the output of coal was far less than it is now, an English economist calculated that forests of an area two and a half times as large as that of the United Kingdom would be required to furnish even a theoretical equivalent of the annual coal produce; practically, of course, the use of wood for an equivalent is out of the question. It was estimated, somewhat later (before 1880), that if the whole area of England were good land, devoted solely to raising forage, it would not support a horse-power equal to that obtained from the English coal mines; and that an area perhaps ten times as large would be required for the mere food supply of human beings of equivalent force.