d then handsomely requested the
philosopher to retain the books in Paris until she required them, and to
constitute himself her librarian, with a yearly salary. In 1773 Diderot
started on an expedition to thank his imperial benefactress in person,
and he passed some months at St Petersburg. The empress received him
cordially. The strange pair passed their afternoons in disputes on a
thousand points of high philosophy, and they debated with a vivacity and
freedom not usual in courts. "_Fi, donc,_" said Catherine one day, when
Diderot hinted that he argued with her at a disadvantage, "_is there any
difference among men?_" Diderot returned home in 1774. Ten years
remained to him, and he spent them in the industrious acquisition of new
knowledge, in the composition of a host of fragmentary pieces, some of
them mentioned above, and in luminous declamations with his friends. All
accounts agree that Diderot was seen at his best in conversation. "He
who only knows Diderot in his writings," says Marmontel, "does not know
him at all. When he grew animated in talk, and allowed his thoughts to
flow in all their abundance, then he became truly ravishing. In his
writings he had not the art of ensemble; the first operation which
orders and places everything was too slow and too painful to him."
Diderot himself was conscious of the want of literary merit in his
pieces. In truth he set no high value on what he had done. It is
doubtful whether he was ever alive to the waste that circumstance and
temperament together made of an intelligence from which, if it had been
free to work systematically, the world of thought had so much to hope.
He was one of those simple, disinterested and intellectually sterling
workers to whom their own personality is as nothing in presence of the
vast subjects that engage the thoughts of their lives. He wrote what he
found to write, and left the piece, as Carlyle has said, "on the waste
of accident, with an ostrich-like indifference." When he heard one day
that a collected edition of his works was in the press at Amsterdam, he
greeted the news with "peals of laughter," so well did he know the haste
and the little heed with which those works had been dashed off.

Diderot died on the 30th of July 1784, six years after Voltaire and
Rousseau, one year after his old colleague D'Alembert, and five years
before D'Holbach, his host and intimate for a lifetime. Notwithstanding
Diderot's peals of laughter at the thought,