129,959. Forrester, H. J. C., (Burgess, H.). July 10, 1918. Resistances f o r heating. A core of refractory material has a groove for the reception of a resist. ance coil so formed as to prevent the escape of the wire from the groove on expansion. As shown in connexion with a core of conical form as described in Specification 129,438, the groove has parallel sides and a rounded bottom and is deeper and slightly wider than the diameter of the wire.