The examples of dramatic art which Diderot gave in his own plays, the _Pere de Famille_ and the _Fils Naturel_, are poor affectations of a style supposed to be natural, and are patently doctrinaire in their design, laboured developments of a moral thesis. One piece in which he paints himself, _Est-il bon? Est-il mechant?_ and this alone, falls little short of being admirable, and yet it fails of true success. A coherent system of thought cannot be found in Diderot's writings, but they are pregnant with ideas. He is deist, pantheist, atheist; he is a materialist--one, however, who conceives matter not as inert, but quick with force. He is edifying and sincere in his morality; and presently his morals become the doctrines of an anarchical licence. All the ideas of his age struggle within him, and are never reduced to unity or harmony; light is never separate in his nature from heat, and light and warmth together give rise to thoughts which are sometimes the anticipations of scientific genius; he almost leaps forward to some of the conclusions of Darwin. His great powers and his incessant energy were not directed to worldly prosperity. Diderot was never rich. The Empress Catherine of Russia magnificently purchased his library, and entrusted him with the books, as her librarian, providing a salary which to him was wealth. He travelled to St. Petersburg to thank her in person for her generous and delicate gift. But her imperial generosity was not greater than his own; he was always ready to lavish the treasures of his knowledge and thought in the service of others; no small fragment of his work was a free gift to his friends, and passed under their name; Holbach and Raynal were among his debtors. His correspondence presents a vivid image of the man and of the group of philosophers to which he belonged; the letters addressed to Mlle. Volland, to whom he was devotedly attached during many years, are frank betrayals of his character and his life. Her loss saddened his last days, but the days of sorrow were few. In July 1784, Diderot died. His reputation and influence were from time to time enhanced by posthumous publications. Other writers of his century impressed their own personalities more distinctly and powerfully upon society; no other writer mingled his genius so completely with external things, or responded so fully and variously to the stimulus of the spirit of his age. II