But when we look into the limits of towns and cities, we find millions of rentable properties of all possible kinds; and every factory, [SN: SOURCES OF INCOME.] every storehouse, every shop and every dwelling house there is a sure source of income to the propertied man. The very sweat-shops, where the working people can not, on an average, live longer than 28 years—even these dens of poison and pestilence are inexhaustible sources of income and profit to their owners. As to the town and city lots, they are all sources of greater or less income to the men who own them. Whether these lots of land are occupied by [SN: SOURCES OF INDIRECT INCOME.] anything or are remaining waste, makes little difference, because as the town population increases, their values also increase in proportion as the city population and its business increase; the owners of properties towards centers of the cities are usually bound to be rich out of the resources of rent. Even a simple house, somewhere about the marginal line of a city or town is usually a source of indirect income to its owner, because he and his family may have a comfortable shelter in it, without which they would pay the rent for another’s house,[52] and would carry on all other expenses of life, just as they do in their own house, in which they save the rental money for some other purposes of living. Now then, whatever property you may think of—whether natural or artificial, whether animate or inanimate, that a person has possession of—it is always wealth, and a source of income in his favor. [SN: WEALTH CREATED BY LABOR.] The natural wealth is the land, wherever it may be in convenient places, it may always provide one or more resources of income in exchange for the application and expense of strength or skill of labor upon it. The artificial wealth includes all capital, whatever it may be, it is capital, if it can assist the labor energy to double, triple or multiple the income and profit, drawn from the natural resource to which the labor-strength is applied. The rentable house or any other building is artificial wealth. And it is also a source of income to its owner who, by a use of skill and by an application of labor energy, can make his source of income give a multiple yield, in return for the expense of his personal strength upon it.