_The Product of the Second Unit of Labor._--We will now introduce a second unit of labor, by doubling the number of workers, without changing the amount of the capital. We must, of course, change the forms of the capital, or it cannot be advantageously used by the larger working force. The buildings will have to be larger, and if they are to be erected with about the same amount of capital as was formerly used, they must be built in a cheaper way. Tools of every sort must be more numerous, and this larger number of tools, if it is to represent the same investment of capital that the former number embodied, must also be simpler and cheaper. The whole equipment of _capital goods_ will have to undergo a complete transmutation; but the essential thing is that the amount of the capital should not be changed. _A Provisional Mode of Measuring Capital._--In measuring the amount of the capital we are obliged to use a unit of cost, and in the illustration we have assumed that the cost can be measured in dollars. The productive fund consisted at the outset of a certain number of dollars invested in productive operations. This is only a provisional mode of measuring it. The money spent really represents sacrifice incurred, and we shall find that the only kind of sacrifice that is available for measuring the cost of goods of any kind is that which is incurred by labor. Ultimate measurements of wealth in all its forms have to be made in terms of labor. Such measurements have presented difficulties, and the attempt to make them has led to serious fallacies. We shall see, in due time, how these fallacies can be avoided.