The booksellers at first spoke of the Encyclopædia as an affair of two million livres. It appeared, however that its cost did not go much beyond one million one hundred and forty thousand livres. The gross return was calculated to be nearly twice as much. The price to the subscriber of the seven volumes up to 1757, of the ten volumes issued in 1765, and of the eleven volumes of plates completed in 1772, amounted to nine hundred and eighty livres,[156] or about forty-three pounds sterling of that date, equivalent in value to more than three times the sum in money of to-day.
The payment received by Diderot is a little doubtful, and the terms were evidently changed from time to time. His average salary, after D'Alembert had quitted him, seems to have amounted to about three thousand livres, or one hundred and thirty pounds sterling, per annum. This coincides with Grimm's statement that the total sum received by Diderot was sixty thousand livres, or about two thousand six hundred pounds sterling.[157] And to think, cried Voltaire, when he heard of Diderot's humble wage, that an army contractor makes twenty thousand livres a day! Voltaire himself had made a profit of more than half a million livres by a share in an army contract in the war of 1734, and his yearly income derived from such gains and their prudent investment was as high as seventy thousand livres, representing in value a sum not far short of ten thousand pounds a year of our present money.
All writers on the movement of illumination in France in the eighteenth century, call our attention to the quick transformation, which took place after the middle of the century, of a speculative or philosophical agitation into a political or social one. Readers often find some difficulty in understanding plainly how or why this metamorphosis was brought about. The metaphysical question which men were then so fond of discussing, whether matter can think, appears very far removed indeed from the sphere of political conceptions. The psychological question whether our ideas are innate, or are solely given to us by experience through the sensations, may strike the publicist as having the least possible to do with the type of a government or the aims of a community. Yet it is really the conclusions to which men come in this region, that determine the quality of the civil sentiment and the significance of political organisation. The theological doctors who persecuted De Prades for suggestions of Locke's psychology, and for high treason against Cartesianism, were guided by a right instinct of self-preservation. De Maistre, by far the most acute and penetrating of the Catholic school, was never more clear-sighted than when he made a vigorous and deliberate onslaught upon Bacon, the centre of his movement against revolutionary principles.[158]