The most important change, however, arose from scientific and mechanical discoveries--the application of heat to the production of motive power. As long as water, which is a non-exhaustive source of motion, was used, the people were scattered over the land; or if segregation took place, it was in the neighborhood of running streams. The application of steam to the propulsion of machinery, and the discovery of engines capable of competing with the human hand, led to the substitution of machine-made fabrics for clothing, in place of homespun articles of domestic manufacture. This led to the employment of farm-laborers in procuring coals, to the removal of many from the rural into the urban districts, to the destruction of the principal employment of the family during the winter evenings, and consequently effected a great revolution in the social system. Many small freeholds were sold, the owners thinking they could more rapidly acquire wealth by using the money representing their occupancy, in trade. Thus the large estates became larger, and the smaller ones were absorbed, while the appearance of greater wealth from exchanging subterranean substances for money, or its representative, gave rise to ostentatious display. The rural population gradually diminished, while the civic population increased. The effect upon the system of landholding was triplicate. First, there was a diminution in the amount of labor applicable to the cultivation of land; second, there was a decrease in the amount of manure applied to the production of food; and lastly, there was an increase in the demand for land as a source of investment, by those who, having made money in trade, sought that social position which follows the possession of broad acres. Thus the descendants of the feudal aristocracy were pushed aside by the modern plutocracy.