\Bar"ret*ter\, n. [OF. bareter to exchange. Cf.
{Barter}.] (Wireless Teleg.)
A thermal cymoscope which operates by increased resistance
when subjected to the influence of electric waves. The
original form consisted of an extremely fine platinum wire
loop attached to terminals and inclosed in a small glass or
silver bulb. In a later variety, called the
{liquid barretter}, wire is replace by a column of liquid in
   a very fine capillary tube.