A temperature measuring apparatus for a top submerged lancing installation, for use in measuring the temperature of a molten bath that includes a slag phase, during a pyro-metallurgical operation conducted in a reactor of the installation, includes a top submerged injecting top submerged injecting lance having at least an outer pipe and an inner pipe. A bore is defined by the inner pipe and an annular passage is defined in part by an inner surface of the outer pipe. The apparatus further includes a pyrometer device of which at least a sensor head part is mounted in relation to the top submerged injecting lance and operable both to receive infrared energy passing longitudinally within the lance from an outlet end of the lance. The sensor head part also is operable to focus the received infrared energy to enable generation of an output signal or display indicative of the temperature of a molten bath in which an outlet end portion of the lance is submerged and from which the infrared energy is received.