UNISON (from ML. unison us, having one sound, from Lat. nuns, one son us, sound). In music, a tone of the same pitch as another. In this sense the term unison is identical with the interval of the prime. The term has, how ever, been extended so as to include all parts performing the same melody, even if some in struments play the tones one or two octaves lower than others.
UNIT (formerly also unite, matte. unity, from Lat. vnitas, oneness, from anus, one). A certain fixed quantity employed for measuring other quantities and for stating their magnitude. Ordinarily a unit is the smallest• complete meas• ure of value, extension, duration, mass, etc., and when employed in measurement involves repeti tion and subdivision. An arbitrary unit is one which may be employed in the form of a con crete standard and which is generally available for reproduction. An example of such a unit is the distance between two marks in gold plugs on a bronze bar in the possession of the British Board of Trade, or the British Standard Yard.
Similarly the meter of the Archives at Paris (see METRIC SYSTEM) is an arbitrary unit. Funda mental units are those selected arbitrarily on account of the ease with which standards can be constructed or reproduced and from which other units can be derived. In the C. G. S. sys tem (q.v.) the fundamental units are those of length, mass, and time, from which units have been derived for area, volume, velocity, force, work, etc., magnetic units, electromagnetic units, etc. In certain instances the derived units in the C. G. S. system may be in such shape that they are not available for general use and either a multiple or a fraction must he employed. Such units are known as practical units. Ex amples of practical units in common use are the ohm, the volt, and the ampere. See C. G. S. SYSTEM ; ?METRIC SYSTEM ; ELECTRICAL UNITS ; MECHANICAL UNITS; WEIGHTS AND MEASURES; MONEY, etc.