The law of diminishing returns applies not to agricultural lands alone but to other classes of land as well. A simple hut erected upon a large building lot in the heart of a prosperous city will furnish to its owner a certain amount of income. This income, however, is not sufficient in view of the value of the lot. A substantial one-family dwelling house would be a better investment. But the value of the lot is too great to permit of its use for this purpose. A large apartment house on the lot will give a reasonable interest on the investment in the house and also pay the rent for the land. If the law of diminishing returns did not exist, the owner could go on indefinitely increasing his expenditure for the house with the result that the income from the house would be increased in the same proportion that the capital expended upon the house was increased. We know, however, that as a matter of fact the owner cannot go on increasing indefinitely his expenditure of capital for this purpose upon a given area of land. Ultimately he will reach a point where the returns do not increase so rapidly as the investment increases. He finds that there is a limit to the amount of capital and labor that can be applied profitably to a given area of city building land. Here he is working under the influence of the law of diminishing returns. The same principle will also be found to be at work in the case of other kinds of land such as mineral land, forest land, public highways, etc.