Radiometer
Pronunciation : Ra`di*om"e*ter
Part of Speech : n.
Etymology : [L. radius radius + -meter: cf. F. radiom?tre.]
Definition : 1. (Naut.)
Defn: A forestaff.
2. (Physics)
Defn: 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 Unabridged Dictionary, 1913