1) An instrument for measuring the intensity of radiant energy
in amounts as small as one millionth of an erg.
It uses the change in resistance of a thin conductor caused by
the heating effect of the radiation.
→ actinometer, → photometer, →
pyrheliometer, → pyrometer,
From Gk. bole "stroke, beam of light," from ballein "to throw" + middle suffix -o- + → -meter..