by purchase, but by way of free gift. Luckily for Diderot,
he was thus generous by temperament, and not because he expected
gratitude. Any necessitous knave with the gift of tears and the mask of
sensibility could dupe and prey upon him. In one case he had taken a
great deal of trouble for one of these needy and importunate clients;
had given him money and advice, and had devoted much time to serve him.
At the end of their last interview Diderot escorts his departing friend
to the head of the staircase. The grateful client then asks him whether
he knows natural history. "Well, not much," Diderot replies; "I know an
aloe from a lettuce, and a pigeon from a humming-bird." "Do you know
about the _Formica leo?_ No? Well, it is a little insect that is
wonderfully industrious; it hollows out in the ground a hole shaped like
a funnel, it covers the surface with a light fine sand, it attracts
other insects, it takes them, it sucks them dry, and then it says to
them, 'M. Diderot, I have the honour to wish you good day.'"[13]

Yet insolence and ingratitude made no difference to Diderot. His ear
always remained as open to every tale of distress, his sensibility
always as quickly touched, his time, money, and service always as
profusely bestowed. I know not whether to say that this was made more,
or that it was made less, of a virtue by his excess of tolerance for
social castaways and reprobates. Our rough mode of branding a man as bad
revolted him. The common appetite for constituting ourselves public
prosecutors for the universe, was to him one of the worst of human
weaknesses. "You know," he used to say, "all the impetuosity of the
passions; you have weighed all circumstance in your everlasting balance;
you pass sentence on the goodness or the badness of creatures; you set
up rewards and penalties among matters which have no proportion nor
relation with one another. Are you sure that you have never committed
wrong acts, for which you pardoned yourselves because their object was
so slight, though at bottom they implied more wickedness than a crime
prompted by misery or fury? Even magistrates, supported by experience,
by the law, by conventions which force them sometimes to give judgment
against the testimony of their own conscience, still tremble as they
pronounce the doom of the accused. And since when has it been lawful for
the same person to be at once judge and informer?"[14]

Such reasoned leniency is the noblest of traits i