e invention of D'Alembert's Dream, and the
sequel, to be as odious as anything since the freaks of filthy Diogenes
in his tub. Two remarks may be made on this strange production. First,
Diderot never intended the dialogues for the public eye. He would have
been as shocked as the Archbishop of Paris himself, if he had supposed
that they would become accessible to everybody who knows how to read.
Second, though they are in form the most ugly and disgusting piece in
the literature of philosophy, they testify in their own way to Diderot's
sincerity of interest in his subject. Science is essentially unsparing
and unblushing, and D'Alembert's Dream plunged exactly into those parts
of physiology which are least fit to be handled in literature. The
attempt to give an air of polite comedy to functions and secretions must
be pronounced detestable, in spite of the dialectical acuteness and
force with which Diderot pressed his point.

[213] _Oeuv._, ii.

It would be impossible, in a book not exclusively designed for a public
of professors, to give a full account of these three dialogues. It is
indispensable to describe their drift, because it is here that Diderot
figures definitely as a materialist. Diderot was in no sense the
originator of the French materialism of the eighteenth century. He was
preceded by Maupertuis, by Robinet, and by La Mettrie; and we have
already seen that when he composed the Thoughts on the Interpretation of
Nature (1754), he did not fully accept Maupertuis's materialistic
thesis. Lange has shown that at a very early period in the movement the
most consistent materialism was ready and developed, while such leaders
of the movement as Voltaire and Diderot still leaned either on deism, or
on a mixture of deism and scepticism.[214] The philosophy of
D'Alembert's Dream is definite enough, and far enough removed alike from
deism and scepticism.

[214] _Gesch. d. Materialismus_, i. 309, 310, etc.

"The thinking man is like a musical instrument. Suppose a clavecin to
have sensibility and memory, and then say whether it would not repeat of
itself the airs that you have played on its keys. We are instruments
endowed with sensibility and memory. Our senses are so many keys,
pressed by the nature that surrounds them, and they often press one
another; and this, according to my judgment, is all that passes in a
clavecin organised as you and I are organised.

"There is only one substance in the world. The ma