Radiometer \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.

Source: Webster's Revised Unabridged Dictionary (1913)