By the invention of machinery, by improvements in skill, by a better division of labour, or by the discovery of new markets, where more advantageous exchanges may be made, a million of men may produce double, or treble the amount of riches, of necessaries, conveniences, and amusements, in one state of society, that they could produce in another, but they will not on that account add any thing to value; for every thing rises or falls in value, in proportion to the facility or difficulty of producing it, or in other words, in proportion to the quantity of labour employed on its production.