what sense is general purchasing power, money and money-funds, of the same denomination as a commodity? Cairnes emphasizes the physical character of both. But surely they are not comparable on the basis of any physical attributes--weight, bulk, etc. Certainly if we look at the concept of demand here given, the physical aspect is simply irrelevant--gold money goes by weight, but what of paper money and credit instruments? And in what sense is even gold money physically of the same denomination with, say, wheat, or hay or base-ball tickets? Not physical quantities, but economic quantities, are relevant here; not weight or bulk, but _value_. By means of a concept of value, as the homogeneous quality of wealth, present in each piece of wealth in definite, quantitative degree, could Cairnes bring about comparability between the "physical" elements in supply and demand. But not otherwise. Only significances, values, are relevant here. Supply and demand presuppose value. It will be interesting to consider the effort to solve the problem of the value of money by means of supply and demand on the lines employed by Mill, where demand for money is defined as quantity of goods to be exchanged, and supply of money as quantity of money times rapidity of circulation, and where physical quantities are treated as the relevant factor, no value concept of the sort here contended for being presupposed. This is, essentially, Mill's method. There is, in this conception, first the difficulty that "quantity of goods to be exchanged" is not a true quantity at all, but is a mere collection of things of different denominations, dozens of eggs, pounds of butter, gallons of milk, etc., incapable of being funded into a quantity.[50] There is, second, the difficulty that increasing the amount of any one of the items in this heterogeneous composite need not increase the "demand" for money, in the sense that it increases the "pull" on money, or tends to increase the supply of money. Yet, under the general doctrine of supply and demand, an increase in demand should be a stimulus to increase in supply. Indeed, it is easy to construct a case where an increase in the quantity of one of the items in this composite, the others remaining unchanged, would actually tend to _repel_ money, to reduce the _supply_ of money. Suppose that one item in America's stock of goods, say cotton, is much increased in quantity, and suppose that cotton has a highly inelastic demand-curve, so that the increased quantity sells for less money than the original quantity.[51] Suppose, too, that cotton is our chief article of export, and that the bulk of our cotton is exported. Would not the "balance of trade" tend to turn against us, so that gold would tend to leave the country, and the supply of money be reduced? There is nothing in the situation assumed to raise the prices of other goods,[52] so that they could exert a counteracting "pull" on money. Europeans, to be sure, having less to pay for cotton,