Abstract: A radiometer horn, an array of such horns, and a method of making a radiometer horn, comprising providing at least two primary walls comprising interior corrugations and fitting into the corrugations at least one secondary wall comprising projections fitting into the corrugations, and wherein no fastener holds any of the at least one secondary walls to the primary walls.

Abstract: A carbon brick/graphite lined furnace for melting, containing and pouring a special purpose slag composed of about 40 percent CaF.sub.2, 30 percent CaO and 30 percent Al.sub.2 O.sub.3 or a slag composed of about 70 percent CaF.sub.2 and 30 percent Al.sub.2 O.sub.3 which has a cylindrical configuration and a roof composed of high alumina ram refractory with openings therein for receiving heating electrodes composed of graphite, for feeding dry slag into the furnace and for exhausting fumes therefrom. The furnace has a pouring spout and the roof can be raised whereby the furnace is turnable about trunions for discharging the molten slag into an electroslag remelting process mold. Both the interior lining and the next surrounding lining are composed of graphite or carbon bricks or a combination thereof. An expansion layer of insulating material, powder alumina, surrounds the second lining. Following this are two further linings of refractory material.