309 I need cite only the instance of the slaves, who called out the hours, thus performing the functions of a clock: _Martial_, VIII. 67; _Juvenal_, X. 216; _Petron._ 26; of the turning of water wheels, in Egypt and Babylon, by human hands. _Strabo_, XVI. 738, XVII., 807. Among the ancients, it required one shepherd, and shepherd boys besides, to take care of twenty sheep. (_Geopon._ XVIII, 1.) In highly cultivated regions, the number ran up to fifty. (_Demosth._, adv. Euerg. et Mnes., 1155.) It seldom passed eighty (_Varro_, De re rust., II. 10, 10. 2, 20), or one hundred (_Cato_, R.R. c. 10); while, recently, five men are sufficient to take care of eighteen hundred sheep. See _Roscher’s_ discourse on the relation of Political Economy to classical antiquity, in the reports of the Royal Saxon Science Association, May, 1849. Also _D. Hume_, Discourses, No. 10. 310 The productive power of each of the factors of production has been over-estimated by some schools. After _Gratian_ (c. i, C. XIII. qu. i), had clearly recognized the necessary coöperation of the three elements, there was in the one-sidedness with which the Reformers emphasized God’s blessing as the only source of wealth, a great over-estimation of the factor nature. The Mercantile System over-estimated the factor capital, in one of its most obvious component parts, money. In later times again: “_La terre est la source ou la matière d’où l’on tire la ichesse; le travail de l’homme est la forme qui la produit. Tous les hommes d’un état subsistent et s’enrichissent aux dépens des propriétaires des terres._” (_Cantillon_, Sur la Nature du Commerce, 1755, I. 33, 55.) _La terre est l’unique source des richesses._ (_Quesnay_, Maximes générales de Gouvernement, 1758, ch. 3.) In another place, indeed, the same writer says: _les revenus sont le produit des terres et des hommes (Grains_, p. 276, Daire), and _Mirabeau_ frequently laid stress on the necessary coöperation of labor and capital. (Landwirthschaftsphilosophie, translation by _Wichmann,_ I, 5.) _Turgot_, Sur la Formation et Distribution des Richesses, § 7. For an excellent refutation of this “Physiocratic” one-sidedness, which, if all men are endowed by nature with equal rights, leads to socialism, see _Canard_, Principes, 6. According to _Gioja_, N. Prospetto, I. 35, the part played by labor, in the production of _Parmesan_ cheese, is a thousand times as great as that played by the soil; and in the production of a Dutch tulip, a hundred thousand times as great. The English are wont, similarly, to over-estimate the relative power of labor. (_Ponocratie_, after _Ancillon_, Essais philosophiques, 1817, II. 327.) “Commerce and trade first spring