As for Rousseau's final years, they began with a period of genuine terror during which he was driven from one place of exile to another, due partly to his overreaction to imagined threats (an admirer wrote years later, "He was forever persecuted, whether by envy or by himself"). What surprised me, however, was the peacefulness of Rousseau's final eight years in Paris. He contracted his social life, enjoyed long walks in the countryside, wrote the magnificent Reveries of the Solitary Walker, and achieved something like the tranquil "sentiment de l'existence" that had always been his ideal.

Calas was the Protestant merchant from Toulouse, who in a monstrous miscarriage of justice had been executed for supposedly murdering his own son for wanting to convert to Catholicism. Thanks to Voltaire's extraordinary efforts Louis XV's council had agreed to review the evidence, and the world's first champion of human rights was hopeful that they would clear Calas's name, even if they could not restore the man to life. And Rousseau—whom Voltaire considered a fellow-traveller in the great cause of Enlightenment—chooses this moment not only to accuse Voltaire of being an atheist but also to reveal that he was the anonymous author of the 'Sermon of the Fifty' (1752), a particularly savage onslaught on the Judaeo-Christian religious tradition? Just when Voltaire was trying to get the Establishment to back him? Voltaire never forgave Rousseau for putting his own campaign against the theatre before the posthumous fate of an innocent man. Thereafter he attacked him openly and violently, revealing to the world for the first time what Rousseau had done with his five children and (in Voltaire's view) exposing him as a hypocrite.