If invention and improvement still go on, the efficiency of labor will be still further increased, and the amount of labor and capital necessary to produce a given result further diminished. The same causes will lead to the utilization of this new gain in productive power for the production of more wealth; the margin of cultivation will be again extended, and rent will increase, both in proportion and amount, without any increase in wages and interest. And, so, as invention and improvement go on, constantly adding to the efficiency of labor, the margin of production will be pushed lower and lower, and rent constantly increased, though population should remain stationary. I do not mean to say that the lowering of the margin of production would always exactly correspond with the increase in productive power, any more than I mean to say that the process would be one of clearly defined steps. Whether, in any particular case, the lowering of the margin of production lags behind or exceeds the increase in productive power, will depend, I conceive, upon what may be called the area of productiveness that can be utilized before cultivation is forced to the next lowest point. For instance, if the margin of cultivation be at 20, improvements which enable the same produce to be obtained with one-tenth less capital and labor will not carry the margin to 18, if the area having a productiveness of 19 is sufficient to employ all the labor and capital displaced from the cultivation of the superior lands. In this case, the margin of cultivation would rest at 19, and rents would be increased by the difference between 19 and 20, and wages and interest by the difference between 18 and 19. But if, with the same increase in productive power the area of productiveness between 20 and 18 should not be sufficient to employ all the displaced labor and capital, the margin of cultivation must, if the same amount of labor and capital press for employment, be carried lower than 18. In this case, rent would gain more than the increase in the product, and wages and interest would be less than before the improvements which increased productive power. Nor is it precisely true that the labor set free by each improvement will all be driven to seek employment in the production of more wealth. The increased power of satisfaction, which each fresh improvement gives to a certain portion of the community, will be utilized in demanding leisure or services, as well as in demanding wealth. Some laborers will, therefore, become idlers and some will pass from the ranks of productive to those of unproductive laborers—the proportion of which, as observation shows, tends to increase with the progress of society.