Abacus. An instrument employed to facilitate arithmetical calculations. The name may be given with propriety to any machine for reckoning with counters, beads, etc., in which one line is made to stand for units, another for tens, and so on. We have here given the form of an abacus, such as we may recommend, for the purpose of teaching the first principles of arithmetic, the only use, as far as we know, to which such an instrument is put in this country. Its length should be about three time its breadth. It consists of a frame, traversed by stiff wires, on which beads or counters are strung so as to move easily. The beads on the first right hand row are units, those on the next tens, and so on. Thus, as it stands, the number 57048 is represented upon the lower part of it.

There is an instrument sold in the toy shops with twelve wires, and twelve beads on each wire, for teaching the multiplication table, and for this purpose much used in our National Infant Schools. The Russians are also much in the habit of performing calculations by strings of beads. In China, however, where the whole system is decimal, this instrument, called in Chinese shwanpan, is universally used. The word Abax was the Greek term for this instrument. Their abacus differs from that described in having only five beads on each line, one of which is distinguished by colour or size from the rest.