Abstract: A continuous metallurgical process such as electroslag refining or continuous casting is continuously monitored by surrounding the area of the melt with a hollow sleeve that contains a continuous helical passageway through which a coolant is continuously passed. The temperature of the coolant is continuously monitored at a plurality of points spaced apart axially of the sleeve, thereby to determine not the temperature of the adjacent metal or slag, but rather the quantity of heat transmitted by that adjacent metal or slag. In this way, the location of the solid metal, the molten metal and the slag, as well as other useful parameters, can be continuously monitored.