Ab′acus. A small frame with wires stretched across it. Each wire contains ten movable balls, which can be shifted backwards or forwards, so as to vary ad libitum the number in two or more blocks. It is used to teach children addition and subtraction. The ancient Greeks and Romans employed it for calculations, and so do the Chinese. The word is derived from the Phœn. abak (dust); the Orientals used tables covered with dust for ciphering and diagrams. In Turkish schools this method is still used for teaching writing. The multiplication table invented by Pythagoras is called Ab′acus Pythagor′icus. (Latin, abacus; Greek, ἄβαξ.)
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