A pyrometer is a thermometer specifically designed to indirectly measure heat. Originally, a pyrometer was meant to measure the temperature of objects above incandescence by way of their visible radiation. Modern pyrometers measure thermal radiation without making direct contact with an object's surface.
Pyrometers are also called "radiation thermometers." The first pyrometer was actually invented by a potter to measure the temperature inside of his kilns. It was produced in 1901 and used a temporary filament placed over the object. Pyrometers are vital components of hot air balloons, certain types of steam boilers, metallurgic and salt bath furnaces, and tuyeres.