One of Diderot's writings composed about our present date (1747), the
Promenade du Sceptique, did not see the light until after his death. His
daughter tells us that a police agent came one day to the house, and
proceeded to search the author's room. He found a manuscript, said,
"Good, that is what I am looking for," thrust it into his pocket, and
went away. Diderot did his best to recover his piece, but never
succeeded.[43] A copy of it came into the hands of Naigeon, and it seems
to have been retained by Malesherbes, the director of the press, out of
goodwill to the author. If it had been printed, it would certainly have
cost him a sojourn in Vincennes.

We have at first some difficulty in realising how he police could know
the contents of an obscure author's desk. For one thing we have to
remember that Paris, though it had been enormously increased in the days
of Law and the System (1719-20), was still of a comparatively manageable
size. In 1720, though the population of the whole realm was only
fourteen or fifteen millions, that of Paris had reached no less a figure
than a million and a half. After the explosion of the System, its
artificial expansion naturally came to an end. By the middle of the
century the highest estimate of the population does not make it much
more than eight hundred thousand.[44] This, unlike the socially
unwholesome and monstrous agglomerations of Paris or London in our own
time, was a population over which police supervision might be made
tolerably effective. It was more like a very large provincial town.
Again, the inhabitants were marked off into groups or worlds with a
definiteness that is now no longer possible. One-fifth of the
population, for instance, consisted of domestic servants.[45] There were
between twenty-eight and thirty thousand professional beggars.[46] The
legal circle was large, and was deeply engrossed by its own interests