permanent fame of an author, are less injurious to his immediate success
than might be expected. A large part of the public does not dislike a
copious admixture of water in its intellectual drink. And Diderot
reconciles the reader to his excessive flow of words by the
effervescence of his enthusiasm. It is because his mind is overfull of
his subject that the sentences burst forth so copiously.

The first writing of Diderot that need engage our attention is his
"Letter on the Blind," published in 1749. This letter deals with the
question, how far congenital deprivation of one of the senses, and
especially blindness, would modify the conceptions of the person
affected; how far the ideas of one born blind would differ from the
ideas of those who can see. The bearing of this question on Locke's
theory that all our ideas are derived from sensation and reflection is
obvious. Diderot, in a manner quite characteristic of him, took pains to
examine the cases of persons who had actually been blind and had
recovered their sight, and where these failed him, supplied their places
by inventions of his own.[Footnote: Condorcet says of Diderot, "faisant
toujours aimer la verite, meme lorsqu'entraine par son imagination il
avait le malheur de la meconnaitre." D'Alembert, _Oeuvres_, i. 79
(_Eloge par Condorcet_). There is a great deal in this remark.
Unless we can enter into the state of mind of men who tell great lies
from a genuine love of abstract truth, we shall never understand the
French Philosophers of the 18th century.]

Diderot's principal witness is Nicholas Saunderson, a blind man with a
talent for mathematics, who between 1711 and 1739 was a professor at the
University of Cambridge. Diderot quotes at some length the atheistic
opinions of Saunderson, giving as his authority the Life of the latter
by "Dr. Inchlif." No such book ever existed, and the opinions are the