The blind mathematician, Dr. Saunderson, adopted a very ingenious device for performing arithmetical operations by the sense of touch.
Small cubes of wood were provided, and in one face of each, nine holes were pierced, thus:
| 1 | 2 | 3 | o | o | o | |
| 4 | 5 | 6 | o | o | o | |
| 7 | 8 | 9 | o | o | o |
These holes represented the nine digits, as in the figure, and to denote any figure, a small peg was inserted into the hole corresponding to it. If the number consisted of several figures, more cubes were used, one for each. A cipher was represented by a peg of different shape from that of the others, and inserted in the central hole.
To perform any arithmetical process, a square board was provided, divided by ridges into recesses of the same width as the cubes, and by this the cubes were retained in the required horizontal and perpendicular lines. Suppose it was necessary to add together the numbers 763, 124, 859, the cubes and pegs would be arranged thus:
THE ABACUS.
This instrument is used for teaching numeration, and the first principles of arithmetic.
