On this point there is absolute agreement between the work done by Smith in England and that carried on at the same time by the Physiocrats in France. Both in foreign and domestic trade producers, merchants, and workmen were hemmed in by a network of restrictions either inherited from the traditions of the Middle Ages or imposed by powerful party interests and upheld by false economic theories. The corporations still existed in the towns; although their regulations could not be applied to industries born after the passing of Elizabeth’s famous law concerning apprenticeship. The Colbertian system, with its mob of officials entrusted with the task of superintending the processes of production, of examining the weight, the length, and the quality of the material employed, was still a grievance with the woollen manufacturers.[229] The fixing of the duration of apprenticeship at seven years, the limitation of the number of apprentices in the principal industries, the obstacles put in the way of the mobility of labour by the Poor Law and by the series of statutes passed since the reign of Elizabeth, fettered the movement of labour and the useful employment of capital. Smith opposed these measures with the whole of his energy. England, unlike France, had fortunately escaped internal restrictions upon trade, but the restraints placed upon foreign trade still kept England and Ireland commercially separated. These checks upon foreign trade proved as irksome in England as they did everywhere else. Manufactured goods from foreign countries were heavily taxed or were prohibited entrance altogether. Certain natural products, _e.g._ French wine, were similarly handicapped; the importation of a number of commodities necessary for national industry was banned; a narrow and oppressive policy regarded the colonies as the natural purveyors of raw materials for the mother-country and the willing buyers of its manufactured goods. Against all this mass of regulations, destined, it was thought, to secure the supremacy of England among other commercial nations, Smith directed his most spirited onslaughts. The fourth book of the _Wealth of Nations_ is an eloquent and vigorous attack upon Mercantilism, admirable alike for the precision and the extent of its learning. It was this section of his work that interested his contemporaries most. For us it would have been the least interesting but for its theory of international trade and its criticism of Protection in general. On this account, however, it is of considerable importance in the study of economic doctrines.