Page:Principles of Political Economy Vol 2.djvu/130

110 for all the gas produced along with it, or vice versâ; the values and prices of the two things will so readjust themselves that both shall find a market.

When, therefore, two or more commodities have a joint cost of production, their natural values relatively to each other are those which will create a demand for each, in the ratio of the quantities in which they are sent forth by the productive process. This theorem is not in itself of any great importance: but the illustration it affords of the law of demand, and of the mode in which, when cost of production fails to be applicable, the other principle steps in to supply the vacancy, is worthy of particular attention, as we shall find in the next chapter but one that something very similar takes place in cases of much greater moment.

§ 2.Another case of value which merits attention, is that of the different kinds of agricultural produce. This is rather a more complex question than the last, and requires that attention should be paid to a greater number of influencing circumstances.

The case would present nothing peculiar, if different agricultural products were either grown indiscriminately and with equal advantage on the same soils, or wholly on different soils. The difficulty arises from two things: first, that most soils are fitter for one kind of produce than another, without being absolutely unfit for any; and secondly, the rotation of crops.

For simplicity, we will confine our supposition to two kinds of agricultural produce; for instance, wheat and oats. If all soils were equally adapted for wheat and for oats, both would be grown indiscriminately on all soils, and their relative cost of production, being the same everywhere, would govern their relative value. If the same labour which grows three quarters of wheat on any given soil, would always grow on that soil five quarters of oats, the three and the five quarters would be of the same value. If again, wheat and oats could