(38). This helps us to understand the difficulty of comparing the money in a country at the present time with what it was in any past century. We must know first of all the difference in our denominations now and then. Sixty-two shillings are now coined from the same quantity of silver as were thirty-seven then. We should know besides what were the regulations regarding weight, fineness, and seignorage. Even if we knew all these facts, we must have besides its power of purchasing labor, before we can attain to accuracy (38).
"Money," he says, "is the best rule of commerce" (Quantulumcunque). It is an imperishable commodity, and it is exposed to smaller fluctuations in value than other commodities. It is, however, absurd to give too much importance to its possession, for the money of a nation is only perhaps a hundredth part of its wealth (20). The rest consists in lands, housing, shipping, furniture, goods, and so on. Remembering this, there ought to be some way of determining what should be the amount of coin in circulation. The general rule to be followed is that it should only be increased when the general wealth of a country increases. In order to measure it exactly he uses one of his favorite methods of computation. We must know the number of people, the amount of their expense annually, and the customary time of settling their accounts. For example, if the rents of lands are eight millions per annum, and they are paid half yearly, there must be four millions of coin to pay them (279).
Although Petty is careful to tell us that money "is but the fat of the body politick," of which there can
