\Ra`di*om"e*ter\, n. [L. radius radius + -meter: cf.
F. radiom[`e]tre.]
1. (Naut.) A forestaff.
2. (Physics) An instrument designed for measuring the
   mechanical effect of radiant energy.
Note: It consists of a number of light discs, blackened on
      one side, placed at the ends of extended arms,
      supported on an a pivot in an exhausted glass vessel.
      When exposed to rays of light or heat, the arms rotate.