If this indeed were true, if the reward of the labourer were always in proportion to what he produced, the quantity of labour bestowed on a commodity, and the quantity of labour which that commodity would purchase, would be equal, and either might accurately measure the variations of other things: but they are not equal; the first is under many circumstances an invariable standard, indicating correctly the variations of other things; the latter is subject to as many fluctuations as the commodities compared with it. Adam Smith, after most ably shewing the insufficiency of a variable medium, such as gold and silver, for the purpose of determining the varying value of other things, has himself, by fixing on corn or labour, chosen a medium no less variable.
Gold and silver are no doubt subject to fluctuations, from the discovery of new and more abundant mines; but such discoveries are rare, and their effects, though powerful, are limited to periods of comparatively short duration. They are subject also to fluctuation, from improvements in the skill and machinery with which the mines may be worked; as in consequence of such improvements, a greater quantity may be obtained with the same labour. They are further subject to fluctuation from the decreasing produce of the mines, after they have yielded a supply to the world, for a succession of ages. But from which of these sources of fluctuation is corn exempted? Does not that also vary, on one hand, from improvements in agriculture, from improved machinery and implements used in husbandry, as well as from the discovery of new tracts of fertile land, which in other countries may be taken into cultivation, and which will affect the value of corn in every market where importation is free? Is it not on the other hand subject to be enhanced in value from prohibitions of importation, from increasing population and wealth, and the greater difficulty of obtaining the increased supplies, on account of the additional quantity of labour which the cultivation of inferior lands requires? Is not the value of labour equally variable; being not only affected, as all other things are, by the proportion between the supply and demand, which uniformly varies with every change in the condition