History is full of great men and women running into each other by coincidences that must have seemed like nothing at the time, but which often throw their biographers into flights of speculation as to what was said, and what was thought, and how each must have reacted. Sometimes the results are seismic, but too often the encounter ends in disappointment. John Keats meeting William Wordsworth was, by all accounts, a social disaster. Elizabeth Gaskell, the industrial novelist, lived on the same street for years as Friedrich Engels, co-author of The Communist Manifesto, without either of them appearing to know who the other was. Edward Thomas and Wilfred Owen would have known each other by sight without either of them having any idea that the other wrote poetry – much less some of the best poetry of World War One.

In the case of Benjamin Franklin meeting Voltaire, however, the charm of the occasion is that the spectators appear to have pre-empted the biographers, and been positively rabid with excitement.

On a Wednesday in April 1778, Benjamin Franklin, at that time a Minister Plenipotentiary to the newly formed United States of America, had with dinner with John Adams, the commissioner and the future President of the United States, and both went afterwards to hear a few papers read at the Academy of Sciences, the premier intellectual gathering in Paris. Benjamin Franklin was already famous throughout France for his discovery of the lightning rod and the electric properties of thunderstorms, in addition to his many literary and philosophical works and his staunch defence of his country’s new independence. Dubbed L’ambassador electrique, he moved among the social circles of Paris with much greater facility than Adams, whose stern republicanism was shocked at the frivolity the French mixed together with the serious affairs of science and diplomacy.

Also attending the Academy of Sciences that night was Voltaire, a voluminous writer whose religious and political scepticism had made his life one long litany of imprisonment in, and banishment from, his native France, but whose many sufferings had never stopped him writing , and served but to increase his fame and popular appeal. Now aged 83 and aware he had only a few months to live, and that the current climate was sympathetic to his opinions, he had broken a three decade sentence of exile and returned to Paris.

According to Adams’ account, the meeting began routinely enough, with D’Alembert, the president, reading eulogies on the recently deceased members of the Academy. But some of the crowd, electrified at the presence of two living legends of the Enlightenment among them, began to demand that Franklin and Voltaire be introduced to one another. The two philosophers bowed formally and spoke to one another, but this was no satisfaction to anyone, and served but to increase the clamour of the audience. As Adams dryly notes:

Neither of our Philosophers seemed to divine what was wished or expected. They however took each other by the hand…. But this was not enough. The Clamour continued, untill the explanation came out “Il faut s’embrasser, a la francoise.” The two Aged Actors upon this great Theatre of Philosophy and frivolity then embraced each other by hugging one another in their Arms and kissing each others cheeks, and then the tumult subsided.

What the two thought of each other, we hardly know, and the meeting led onto nothing new in the careers of these two titans of the Enlightenment, whose greatest triumphs were now behind them. All the same, one would have loved to have been there.