“ In his work entitled Didascalocophus, or the Deaf and Dumb Man’s Tutor (Oxford, 1680) , he explained, for the first time, the hand alphabet for the deaf and dumb, though he does not claim to have invented this method of communication. Twenty years before the publication of his Didascalocophus, Dalgarno had given to the world a very ingenious piece entitled Ars Signorum (1661) , dividing ideas into seventeen classes, to be represented by the letters of the Latin alphabet with the addition of two Greek characters. ”