from the mine to the market, so when they were brought thither they could purchase or command less labour; and this revolution in their value, though perhaps the greatest, is by no means the only one of which history gives some account.

But as a measure of quantity, such as the natural foot, fathom, or handful, which is continually varying in its own quantity, can never be an accurate measure of the quantity of other things; so a commodity which is itself continually varying in its own value, can never be an accurate measure of the value of other commodities. Equal quantities of labour, at all times and places, may be said to be of equal value to the labourer. In his ordinary state of health, strength and spirits; in the ordinary degree of his skill and dexterity, he must always laydown the same portion of his ease, his