We have already said so much of the great and important group of articles on arts and trades, that it is unnecessary to add anything further as to Diderot’s particular share in them.  He visited all the workshops in Paris; he sent for information and specifications to the most important seats of manufacture in the kingdom; he sometimes summoned workmen from the provinces to describe to him the paper works of Montargis, and the silk works and velvet works of Lyons.[180] Much of Diderot’s work, even on great practical subjects, was, no doubt, the reproduction of mere book-knowledge acquired at second-hand.  Take, for instance, Agriculture, which was undoubtedly the most important of all subjects for France at that date, as indeed at every other date.  There are a dozen pages of practical precepts, for which Diderot was probably indebted to one of the farmers at Grandval.  After this, he fills up the article with about twenty pages in which he gives an account of the new system of husbandry, which our English Jethro Tull described to an unbelieving public between 1731 and 1751.  Tull’s volume was translated into French by Duhamel, with notes and the record of experiments of his own; from this volume Diderot drew the pith of his article.  Diderot’s only merit in the matter—­and it is hardly an inconsiderable one in a world of routine—­is that he should have been at the pains to seek the newest lights, and above all that he should have urged the value of fresh experiments in agriculture.  Tull was not the safest authority in the world, but it is to be remembered that the shrewd-witted Cobbett thought his ideas on husbandry worth reproducing, seventy years after Diderot had thought them worth compiling into an article.

It was not merely in the details of the practical arts that Diderot wrote from material acquired at second-hand.  The article on the Zend-Avesta is taken from the Annual Register for 1762.  The long series of articles on the history of philosophy is in effect a reproduction of what he found in Bayle, in Deslandes, and in Brucker.  There are one or two considerable exceptions.  Perhaps the most important is under the heading of Spinosa, to which we shall return presently.  The article on Hobbisme contains an analysis, evidently made by the writer’s own hand, of the bulk of Hobbes’s propositions; it is scarcely, however, illuminated by a word of criticism.  If we turn to the article on Societe, it is true, we find Hobbes’s view of the relations between the civil and temporal powers tolerably effectively combated, but even here Diderot hardly does more than arm himself with the weapons of Locke.