Cooling air passages are formed in the wall of an exhaust casing connected to a turbine casing of a gas turbine. The terminal box includes a terminal box body embedded in a wall and for providing a space for installation of a terminal and a switch to connect an incoming electric wire, telephone line, designated Internet line, antenna line, or the like, and a cover coupled to the front of the terminal box body. Scribe marks 50 defined on the lower surface of the bridge provide indica to guide a horseshoer in grinding the bridge to provide greater flexibility. The target region can be outside the spectrometer, with ambient air in between used for the self-focusing.