the more disinterestedly scientific parts of his contribution. People
were not strongly agitated by the question whether a blind man who had
learned to distinguish a sphere from a cube by touch, would instantly
identify each of them if he received sight.[67]

The question whether a blind man has as good reasons for believing in
the existence of a God as a man with sight can find, was of more vivid
interest. As a matter of fact, Diderot's treatment of the narrower
question (pp. 324, etc.) is more closely coherent than his treatment of
the wider one, for the simple reason that the special limitation of
experience in the born-blind cannot fairly be made to yield any decisive
evidence on the great, the insoluble enigma.

Here, as in the other part of his essay, Diderot followed the method of
interrogating the blind themselves. In this instance, he turned to the
most extraordinary example in history, of intellectual mastery and
scientific penetration in one who practically belonged to the class of
the born-blind; and this too in dealing with subjects where sight might
be thought most indispensable. From 1711 to 1739 one of the professors
of mathematics at Cambridge was Nicholas Saunderson, who had lost his
sight before he was twelve months old. He was a man of striking mental
vigour, an original and efficient teacher, and the author of a book upon
algebra which was considered meritorious in its day. His knowledge of
optics was highly remarkable. He had distinct ideas of perspective, of
the projections of the sphere, and of the forms assumed by plane or
solid figures in certain positions. For performing computations he
devised a machine of great ingenuity, which also served the purpose,
with certain modifications, of representing geometrical diagrams. In
religion he was a sceptic or something more, and in his last hours
Diderot supposes him to have engaged in a discussion with a minister of