The thought went no further, in Diderot’s mind, than this pathetic ejaculation.  He left it to the next generation, to Condorcet and others, to attack the problem practically; effectively to assert the true theory that we must look to social emancipation in women, and moral discipline in men, to redress the physical disadvantages.  Meanwhile Diderot deserves credit for treating the position and character of women in a civilised society with a sense of reality; and for throwing aside those faded gallantries of poetic and literary convention, that screen a broad and dolorous gulf.

CHAPTER IV.

THE NEW PHILOSOPHY.

It is a common prejudice to treat Voltaire as if he had done nothing save write the Pucelle and mock at Habakkuk.  Every serious and instructed student knows better.  Voltaire’s popularisation of the philosophy of Newton (1738) was a stimulus of the greatest importance to new thought in France.  In a chapter of this work he had explained with his usual matchless terseness and lucidity Berkeley’s theory of vision.  The principle of this theory is, as every one knows, that figures, magnitudes, situations, distances, are not sensations but inferences; they are not the immediate revelations of sight, but the products of association and intellectual construction; they are not directly judged by vision, but by imagination and experience.  If this be so, neither situation, nor distance, nor magnitude, nor figure, would be at once discerned by one born blind, supposing him suddenly to receive sight.  Voltaire then describes the results of the operation performed by Cheselden (1728) on a lad who had been blind from his birth.  This experiment was believed to confirm all that Locke and Berkeley had foreseen, for it was long before the patient could distinguish objects by size, distance, or shape.[61] Condillac had renewed the interest which Voltaire had first kindled in the subject, by referring to Cheselden’s experiment in his first work, which was published in 1746.[62]

It happened that in 1748 Reaumur couched the eyes of a girl who had been born blind.  Diderot sought to be admitted to the operation, but the favour was denied him, and he expressed his resentment in terms which, as we shall see, cost him very dear.  As he could not witness the experiment, he began to meditate upon the subject, and the result was the Letter on the Blind for the Use of those who See. published in 1749—­the date, it may be observed in passing, of another very important work in the development of materialistic speculation, David Hartley’s Observations on man, his frame, his duty, and his expectations.  Diderot’s real disappointment at not being admitted to the operation was slight.  In a vigorous passage he shows the difficulties in the way of conducting such an experiment under the conditions necessary to make it conclusive.  To prepare the born-blind to answer philosophical interrogatories