Page:Popular Science Monthly Volume 33.djvu/667

 with a perpendicular movement, which, for the formation of the written signs, is combined with a horizontal governed by the key-board, which moves a crank-screw. The paper is borne upon a carriage which changes place from line to line. Each graphic sign is numbered according to the needles that have to be struck to produce it. To form, for instance, the letter H with this machine, twenty marks have to be made, with as many strokes on the keys, and perhaps half as many displacements of the horizontal. The machine is too complicated to be practical.

Experiments were made by Hassenfratz in 1783, and Challaut in 1820, in using thick inks in writing which should produce a relief on the paper after they had dried; and the Abbé Vitali manufactured an ink which would give relief enough to be felt by the

 1. Ballu's tablet: 1' detail of squares, a pin. 2. Oury's tablet: 2' detail of the octagons, red pins.

finger of the blind man. It has not been found convenient for writing, but has been applied with advantage to the drawing of geometrical figures, and for maps. Some of the most successful maps have been prepared by M. Trouillard, who uses linoleum, and indicates the rivers by iron wires, and mountains by more or less prominent undulations. The place of each city, the name of which is indicated by the initial letter in "Braille," is marked by a peg split at the top. A thread attached to the point that