One or two trifling points of literary interest may be noticed in the Letter on the Blind.  Diderot refers to “the ingenious expression of an English geometer that God geometrises” (p. 294).  He is unaware apparently of the tradition which attributes the expression to Plato, though it is not found in Plato’s writings.  Plutarch, I believe, is the first person who mentions the saying, and discusses what Plato exactly meant by it.  In truth, it is one of that large class of dicta which look more ingenious than they are true.  There is a fine Latin passage by Barrow on the mighty geometry of the universe, and the reader of the Religio Medici (p. 42) may remember that Sir Thomas Browne pronounces God to be “like a skilful geometrician.”

An odd coincidence of simile is worth mentioning.  Diderot says “that great services are like large pieces of money, that we have seldom any occasion to use.  Small attentions are a current coin that we always carry in our hands.”  This is curiously like the saying in the Tatler that “A man endowed with great perfections without good breeding is like one who has his pockets full of gold, but wants change for his ordinary occasions.”  Yet if Diderot had read the Tatler, he would certainly have referred to the story in No. 55, how William Jones of Newington, born blind, was brought to sight at the age of twenty—­a story told in a manner after Diderot’s own heart.

II.

It is proper in this place to mention a short philosophic piece which Diderot wrote in 1751, his Letter on the Deaf and Dumb for the Use of those who Hear and Talk.  This is not, like the Letter on the Blind, the examination of a case of the Intellect deprived of one or more of the senses.  It is substantially a fragment, and a very important fragment, on AEsthetics, and as such there will be something to say about it in another chapter.  But there are, perhaps, one or two points at which the Letter on the Deaf and Dumb touches the line of thought of the Letter on the Blind.

The Letter opens on the question of the origin and limits of inversion in language.  This at once leads to a discussion of the natural order of ideas and expressions, and that original order, says Diderot, we can only ascertain by a study of the language of gesture.  Such a study can be pursued either in assiduous conversation with one who has been deaf and dumb from birth, or by the experiment of a muet de convention, a man who foregoes the use of articulate sounds for the sake of experiment as to the process of the formation of language.  Generalising this idea, Diderot proceeds to consider man as distributed into as many distinct and separate beings as he has senses.  “My idea would be to decompose a man, so to speak, and to examine what he derives from each of the senses with which he is endowed.  I have sometimes amused myself with this kind of metaphysical