little to fulfil the promise of that work. He had retired to the country
house of Madame du Châtelet, where he had devoted himself to science,
play-writing, and the preparation of a universal history. His reputation
had increased; for it was in these years that he produced his most
popular tragedies--_Zaïre, Mérope, Alzire_, and _Mahomet_--while a
correspondence carried on in the most affectionate terms with Frederick
the Great yet further added to his prestige; but his essential genius
still remained quiescent. Then at last Madame du Châtelet died and
Voltaire took the great step of his life. At the invitation of Frederick
he left France, and went to live as a pensioner of the Prussian king in
the palace at Potsdam. But his stay there did not last long. It seemed
as if the two most remarkable men in Europe liked each other so well
that they could not remain apart--and so ill that they could not remain
together. After a year or two, there was the inevitable explosion.
Voltaire fled from Prussia, giving to the world before he did so one of
the most amusing _jeux d'esprit_ ever written--the celebrated _Diatribe
du Docteur Akakia_--and, after some hesitation, settled down near the
Lake of Geneva. A few years later he moved into the _château_ of Ferney,
which became henceforward his permanent abode.

Voltaire was now sixty years of age. His position was an enviable one.
His reputation was very great, and he had amassed a considerable
fortune, which not only assured him complete independence, but enabled
him to live in his domains on the large and lavish scale of a country
magnate. His residence at Ferney, just on the border of French
territory, put him beyond the reach of government interference, while he
was yet not too far distant to be out of touch with the capital. Thus
the opportunity had at last come for the full display of his powers. And
those powers were indeed extraordinary. His character was composed of a
strange amalgam of all the most contradictory elements in human nature,