no where under values the services which these natural agents and machinery perform for us, but he very justly distinguishes the nature of the value which they add to commodities they are serviceable to us, by increasing the abundance of productions, by making men richer, by adding to value in use; but as they perform their work gratuitously, as nothing is paid for the use of air, of heat, and of water, the assistance which they afford us, adds nothing to value in exchange.