The increasing abundance of food, in consequence of the increasing improvement and cultivation, must necessarily increase the demand for every part of the produce of land which is not food, and which can be applied either to use or to ornament. In the whole progress of improvement, it might, therefore, be expected there should be only one variation in the comparative values of those two different sorts of produce. The value of that sort which sometimes does, and sometimes does not afford rent, should constantly rise in proportion to that which always affords some rent. As art and industry advance, the materials of clothing and lodging, the useful fossils and materials of the earth, the precious metals and the precious stones, should gradually come to be more and more in demand, should gradually exchange for a greater and a greater quantity of food; or, in other words, should gradually become dearer and dearer. This, accordingly, has been the case with most of these things upon most occasions, and would have been the case with all of them upon all occasions, if particular accidents had not, upon some occasions, increased the supply of some of them in a still greater proportion than the demand. The value of a free-stone quarry, for example, will necessarily increase with the increasing improvement and population of the country round about it, especially if it should be the only one in the neighbourhood. But the value of a silver mine, even though there should not be another within a thousand miles of it, will not necessarily increase with the improvement of the country in which it is situated. The market for the produce of a free-stone quarry can seldom extend more than a few miles round about it, and the demand must generally be in proportion to the improvement and population of that small district; but the market for the produce of a silver mine may extend over the whole known world. Unless the world in general, therefore, be advancing in improvement and population, the demand for silver might not be at all increased by the improvement even of a large country in the neighbourhood of the mine. Even though the world in general were improving, yet if, in the course of its improvements, new mines should be discovered, much more fertile than any which had been known before, though the demand for silver would necessarily increase, yet the supply might increase in so much a greater proportion, that the real price of that metal might gradually fall; that is, any given quantity, a pound weight of it, for example, might gradually purchase or command a smaller and a smaller quantity of labour, or exchange for a smaller and a smaller quantity of corn, the principal part of the subsistence of the labourer. The great market for silver is the commercial and civilized part of the world.