The cause of the surplus-profit, then, arises here from the capital itself (which includes the labour set in motion by it) whether it be due to the greater magnitude of capital employed or to its more efficient application; and, as a matter of fact, there is no particular reason why all capital in the same production sphere should not be invested in the same manner. On the contrary, the competition between capitals tends to cancel these differences more and more. The determination of value by the socially necessary labour-time asserts itself through the cheapening of commodities and the compulsion to produce commodities under the same favourable conditions. But matters are different with the surplus-profit of an industrial capitalist who makes use of the waterfall. The increased productiveness of the labour used by him comes neither from the capital and labour itself, nor from the mere application of some natural force different from capital and labour but incorporated in the capital. It arises from the greater natural productiveness of labour bound up with the application of a force of Nature, but not a force of Nature that is at the command of all capital in the same sphere of production, as for example the elasticity of steam. In other words, its application is not to be taken for granted whenever capital is generally invested in this sphere of production. On the contrary, it is a monopolisable force of Nature which, like the waterfall, is only at the command of those who have at their disposal particular portions of the earth and its appurtenances. It is by no means within the power of capital to call into existence this natural premise for a greater productivity of labour in the same manner as any capital may transform water into steam. It is found only locally in Nature and, wherever it does not exist, it cannot be established by a definite investment of capital. It is not bound to goods which labour can produce, such as machines and coal, but to specific natural conditions prevailing in certain portions of land. Those manufacturers who own waterfalls exclude those who do not from using this natural force, because land, and particularly land endowed with water-power, is scarce. This does not prevent the amount of water-power available for industrial purposes from being increased, even though the number of natural waterfalls in a given country is limited. The waterfall may be harnessed by man in order to fully exploit its motive force. If such exists, the water-wheel may be improved so as to make use of as much of the water-power as possible; where the ordinary wheel is not suitable for the water-supply, turbines may be used, etc. The possession of this natural force constitutes a monopoly in the hands of its owner; it is a condition for an increase in the productiveness of the invested capital that cannot be established by the production process of the capital itself; [33] this natural force, which can be monopolised in this manner, is always bound to the land. Such a natural force does not belong to the general conditions of the sphere of production in question, nor to those conditions of the latter which may be generally established.