In addition to his scientific labours, Pallas was engaged by Catherine in drawing up comparative vocabularies of the languages spoken by all the various nations in the Russian empire; but was restrained, in the execution of this plan, to follow exactly in the track pointed out by his mistress. He was likewise chosen member of the committee employed, in 1777, in compiling a new topography of the empire; and had the honour of instructing Alexander, the late despot of Russia, and his brother Constantine, in natural history. But, notwithstanding all these marks of distinction, and many others of equal importance, our traveller experienced the truth, that happiness is incompatible with dependence of every kind. His travelling habits, too, rendered a sedentary life irksome to him; but what still further disgusted him with Petersburg, was the crowd of fashionable but absurd people who thronged his house, imagining, perhaps, they were doing him an honour by consuming his time. To escape from this species of persecution, he took advantage of the invasion of the Crimea, to visit new countries; and during the years 1793 and 1794, traversed the southern provinces of the empire at his own expense. He even skirted the frontiers of Circassia, but, with his usual prudence, avoided the dangers which would have attended a journey into that country. He then proceeded into the Crimea, through which Potemkin was leading the empress as a spectacle of contempt and scorn to all mankind; and was so captivated by a passing glance at its splendid scenery, that, on his return to Petersburg, he solicited and obtained permission to retire thither.