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Rh contemplated in this estimate; perhaps, therefore, not at all. 63. Now, in order to show the manner in which price is expressed in terms of a currency, we must assume these four quantities to be known, and "the estimate of desirableness," commonly called the Demand, to be certain. We will take the number of persons at the lowest. Let A and B be two labourers who "demand," that is to say, have resolved to labour for, two articles, a and b. Their demand for these articles (if the reader likes better, he may say their need) is to be conceived as absolute, their existence depending on the getting these two things. Suppose, for instance, that they are bread and fuel, in a cold country, and let a represent the least quantity of bread, and b the least quantity of fuel, which will support a man's life for a day. Let a be producible by an hour's labour, but b only by two hours' labour.

Then the cost of a is one hour, and of b two (cost, by our definition, being expressible in terms of time). If, therefore, each man worked both for his corn and fuel, each would have to work three hours a day. But they divide the