These are EXTRACTIVE INDUSTRY,--including all the semi-barbarous functions mentioned above,--COMMERCIAL INDUSTRY, MANUFACTURING, INDUSTRY, AGRICULTURAL INDUSTRY. And it is for a profound reason that the learned author placed agriculture last in the list. For, despite its great antiquity, it is certain that this industry has not kept pace with the others, and the succession of human affairs is not decided by their origin, but by their entire development. It may be that agricultural industry was born before the others, and it may be that all were contemporary; but that will be deemed of the latest date which shall be perfected last. Thus the very nature of things, as well as his own wants, indicates to the laborer the order in which he should effect the production of the values that make up his well-being. Our law of proportionality, then, is at once physical and logical, objective and subjective; it has the highest degree of certainty. Let us pursue the application. Of all the products of labor, none perhaps has cost longer and more patient efforts than the calendar. Nevertheless, there is none the enjoyment of which can now be procured more cheaply, and which, consequently, by our own definitions, has become more necessary. How, then, shall we explain this change? Why has the calendar, so useless to the early hordes, who only needed the alternation of night and day, as of winter and summer, become at last so indispensable, so unexpensive, so perfect? For, by a marvelous harmony, in social economy all these adjectives are interconvertible. How account, in short, by our law of proportion, for the variability of the value of the calendar? In order that the labor necessary to the production of the calendar might be performed, might be possible, man had to find means of gaining time from his early occupations and from those which immediately followed them. In other words, these industries had to become more productive, or less costly, than they were at the beginning: which amounts to saying that it was necessary first to solve the problem of the production of the calendar from the extractive industries themselves.