These letters to Mlle. Voland form the most characteristic and intimately personal record of himself that Diderot left. He was forty years old when the correspondence began, and it lasted for more than twenty years. Of Sophie Voland almost nothing is known; we only catch glimpses of her as a woman of wide sympathies and decided intelligence, neither very young nor pretty, and wearing spectacles; she lived with her family, who were clearly more orthodox and conventional than herself, and must not, as Diderot frequently hints, see everything that he writes. Of the depth and reality of his affection for her there is no doubt; his editors have discussed the question as to whether this affection was throughout of the nature of friendship only, or whether, according to the phrase of Sainte-Beuve, an hour’s passion had served as the golden key to the most precious and intimate secrets of friendship. This may be as it will; Diderot had found some one in whose presence he could show himself, without reserve or precaution, on every side of his manifold nature, and he was always tenderly grateful to the woman who had procured him this sweetest of pleasures. “My Sophie is both man and woman,” he wrote to her, “when she pleases;” as such he always addressed her, pouring out recklessly all that happened to be in his head, narrating the incidents of the day, telling what he was thinking about or projecting, repeating current scandal or sometimes not quite decent story, flashing instinctively into wise or witty reflection; always with a swift, almost unconscious pen, forgetting now and again what he has already said. It is only in these letters, where he is, as he says, “rendering an account of all the moments of a life that belongs to you,” that we realize the personal charm, the exuberant strength and at the same time the weakness of the man who in the midst of his manifold energies bursts out: “A delicious repose, a sweet book to read, a walk in some open and solitary spot, a conversation in which one discloses all one’s heart, a strong emotion that brings the tears to one’s eyes and makes the heart beat faster, whether it comes of some tale of generous action or of a sentiment of tenderness, of health, of gaiety, of liberty, of indolence--there is the true happiness, nor shall I ever know any other.”