"Mr. Malthus says, " It has been justly observed by Adam Smith that no equal quantity of productive labour employed in manufactures can ever occasion so great a reproduction as in agriculture. " If Adam Smith speaks of value, he is correct; but if he speaks of riches, which is the important point, he is mistaken; for he has himself defined riches to consist of the necessaries, conveniences, and enjoyments of human life. One set of necessaries and conveniences admits of no comparison with another set; value in use cannot be measured by any known standard; it is differently estimated by different persons."