As a matter of fact, when a rise in the value of hops or of corn is spoken of, who ever thinks about the changes which may have taken place in the values of iron, flax, or cabbages? For short periods, we consider money as nearly a correct measure of the values of commodities, as well as of their prices; and if hops and corn have risen in this measure, we do not hesitate to say that their values have risen, without the least reference to cloths, calicoes, or cambrics. This is a clear proof that, in general, when we speak of the variations in the values of commodities, we do not measure them by the variations in their general power of purchasing, but by some sort of standard which we think better represents the varying estimation in which they are held, determined at all times by the state of the supply compared with the demand, and, on an average, by the elementary costs of production. The only variations in the general power of a commodity to purchase, which are susceptible of a distinct and definite measure, are those which arise from causes which affect the commodity itself, and not from the causes which affect the innumerable articles against which it is capable of being exchanged. In speaking, therefore, of the variations in the value of particular commodities, it is not only more accordant with the accustomed meaning attached to the expression, but absolutely necessary with a view to precision, to consider them as exclusively proportioned to, and measured by, the amount of the causes of value operating upon themselves. Mr. Ricardo, therefore, quite consistently with his own hypothesis, considers a commodity, the producing labour of which has doubled, as having increased to double its former value. It has increased in relation to a standard which, according to him, is the sole cause of value; it will command just double the quantity of all those commodities which have not altered in their producing value; and if it will not command just double the quantity of other commodities, it is not because it will not command just double the _value_ which it did before, but because, on account of the changes in the producing labour of the other commodities, double the quantity of them has become more or less than double the value.