c versatility, he turned from ethical speculation to the
composition of a volume of stories, the _Bijoux indiscrets_ (1748),
gross without liveliness, and impure without wit. In later years he
repented of this shameless work, just as Boccaccio is said in the day of
his grey hairs to have thought of the sprightliness of the _Decameron_
with strong remorse. From tales Diderot went back to the more congenial
region of philosophy. Between the morning of Good Friday and the evening
of Easter Monday he wrote the _Pensees philosophiques_ (1746), and he
presently added to this a short complementary essay on the sufficiency
of natural religion. The gist of these performances is to press the
ordinary rationalistic objections to a supernatural revelation; but
though Diderot did not at this time pass out into the wilderness beyond
natural religion, yet there are signs that he accepted that less as a
positive doctrine, resting on grounds of its own, than as a convenient
point of attack against Christianity. In 1747 he wrote the _Promenade du
sceptique_, a rather poor allegory--pointing first to the extravagances
of Catholicism; second, to the vanity of the pleasures of that world
which is the rival of the church; and third, to the desperate and
unfathomable uncertainty of the philosophy which professes to be so high
above both church and world.

Diderot's next piece was what first introduced him to the world as an
original thinker, his famous _Lettre sur les aveugles_ (1749). The
immediate object of this short but pithy writing was to show the
dependence of men's ideas on their five senses. It considers the case of
the intellect deprived of the aid of one of the senses; and in a second
piece, published afterwards, Diderot considered the case of a similar
deprivation in the deaf and dumb. The _Lettre sur les sourds et muets_,
however, is substantially a digressive examination of some points in
aesthetics. The philosophic significance of the two essays is in the
advance they make towards the principle of Relativity. But what
interested the militant philosophers of that day was an episodic
application of the principle of relativity to the master-conception of
God. What makes the _Lettre sur les aveugles_ interesting is its
presentation, in a distinct though undigested form, of the modern theory
of variability, and of survival by superior adaptation. It is worth
noticing, too, as an illustration of the comprehensive freedom with
which D