These different sorts of rude produce may be divided into three classes. The first comprehends those which it is scarce in the power of human industry to multiply at all. The second, those which it can multiply in proportion to the demand. The third, those in which the efficacy of industry is either limited or uncertain. In the progress of wealth and improvement, the real price of the first may rise to any degree of extravagance, and seems not to be limited by any certain boundary. That of the second, though it may rise greatly, has, however, a certain boundary, beyond which it cannot well pass for any considerable time together. That of the third, though its natural tendency is to rise in the progress of improvement, yet in the same degree of improvement it may sometimes happen even to fall, sometimes to continue the same, and sometimes to rise more or less, according as different accidents render the efforts of human industry, in multiplying this sort of rude produce, more or less successful. First Sort.—The first sort of rude produce, of which the price rises in the progress of improvement, is that which it is scarce in the power of human industry to multiply at all. It consists in those things which nature produces only in certain quantities, and which being of a very perishable nature, it is impossible to accumulate together the produce of many different seasons. Such are the greater part of rare and singular birds and fishes, many different sorts of game, almost all wild-fowl, all birds of passage in particular, as well as many other things. When wealth, and the luxury which accompanies it, increase, the demand for these is likely to increase with them, and no effort of human industry may be able to increase the supply much beyond what it was before this increase of the demand. The quantity of such commodities, therefore, remaining the same, or nearly the same, while the competition to purchase them is continually increasing, their price may rise to any degree of extravagance, and seems not to be limited by any certain boundary. If woodcocks should become so fashionable as to sell for twenty guineas a-piece, no effort of human industry could increase the number of those brought to market, much beyond what it is at present. The high price paid by the Romans, in the time of their greatest grandeur, for rare birds and fishes, may in this manner easily be accounted for. These prices were not the effects of the low value of silver in those times, but of the high value of such rarities and curiosities as human industry could not multiply at pleasure. The real value of silver was higher at Rome, for sometime before, and after the fall of the republic, than it is through the greater part of Europe at present.