bolometer An instrument for measuring intensity of thermal radiation. It consists of very thin platinum strips, joined together in series, suitably mounted in a frame. The strips are coated with platinum black in order that they may absorb maximum amount of thermal radiation. The grid so constructed has an appreciable amount of resistance 50 ohms, but low thermal capacity for the given surface area. This makes the bolometer reach the equilibrium in a shortest possible time, when exposed to radiation. The grid is enclosed in a tube so as to protect it from air current and stray radiations. The change in the resistance of the grid is measured using a bridge and sensitive galvanometer, from which the intensity of the radiation is estimated.