After three months of captivity, Diderot was released. The booksellers who were interested in the Encyclopaedia were importunate with the authorities to restore its head and chief to an enterprise that stirred universal curiosity.[89] For the first volume of that famous work was now almost ready to appear, and expectation was keen. The idea of the book had occurred to Diderot in 1745, and from 1745 to 1765 it was the absorbing occupation of his life. Of the value and significance of the conception underlying this immense operation, I shall speak in the next chapter. There also I shall describe its history. The circumstances under which these five-and-thirty volumes were given to the world mark Diderot for one of the few true heroes of literature. They called into play some of the most admirable of human qualities. They required a laboriousness as steady and as prolonged, a wariness as alert, a grasp of plan as firm, a fortitude as patient, unvarying, and unshaken, as men are accustomed to applaud in the engineer who constructs some vast and difficult work, or the commander who directs a hardy and dangerous expedition. CHAPTER V. THE ENCYCLOPAEDIA. The history of the encyclopaedic conception of human knowledge is a much more interesting and important object of inquiry than a list of the various encyclopaedic enterprises to be found in the annals of literature. Yet it is proper here to mention some of the attempts in this direction, which preceded our memorable book of the eighteenth century. It is to Aristotle, no doubt, that we must look for the first glimpse of the idea that human knowledge is a totality, whose parts are all closely and organically connected with one another. But the idea that only dawned in that gigantic understanding was lost for many centuries. The compilations of Pliny are not in a right sense encyclopaedic, being presided over by no definite idea of informing order. It was not until the later middle age that any attempt was made to present knowledge as a whole. Albertus Magnus, "the ape of Aristotle" (1193-1280), left for a season the three great questions of the existence of universals, of the modes of the existence of species and genus, and of their place in or out of the bosom of the individuals, and executed a compilation of such physical facts as had been then discovered.[90] A more distinctly encyclopaedic work was the book of Vincent de Beauvais (_d._ 1264), called _Speculum naturale, morale, doctrinale, et historiale_--a compilation from Aquinas in some parts, and from Aristotle in others. Hallam mentions three other compilations of the thirteenth and fourteenth centuries, and observes that their laborious authors did not much improve the materials which they had amassed in their studies, though they sometimes arranged them conveniently. In the mediaeval period, as he remarks, the want of capacity to discern probable truths was a very great drawback from the value of their compilations.[91]