WRITING-MACHINES FOR THE BLIND. 



649 



ing with a perpendicular movement, which, for the formation of 

 the written signs, is combined with a horizo7ital 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 ma- 

 chine, twenty marks have to be made, with as many strokes on 

 the keys, and perhaps half as many displacements of the horizon- 

 tal. 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 re- 

 lief on the paper after they had dried ; and the Abbe Vitali manu- 

 factured an ink which would give relief enough to be felt by the 



Fig. 5.— Calculating Instruments for the Use cf the Blind. 1. Ballu's tablet: 

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



detail of 



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 indi- 



