Heating apparatus having ellipsoidal reflecting mirror

A heating apparatus comprising divided ellipsoidal reflecting mirror means having a first mirror member with a first focal point and a second mirror member with a second focal point, said first and second focal points being located on a common axis (X), a single heat source disposed in the vicinity of said first focal point within said reflecting mirror means, means for holding a substance to be heated by the radiation generated by said heat source so that said substance is disposed in the vicinity of said second focal point within said reflecting mirror means, a substantially straight additional spacer member (16 or 49) having a given length in the direction of the common axis (X), said additional spacer member being interposed between said first and second mirror members to correspondingly increase the spacing between the first and second focal points, said heat source having a center located in a first position spaced from said first focal point and wherein said substance to be heated has a molten zone with a center (28) located at a second position spaced apart from said second focal point to obtain a desired substantially uniform temperature distribution all around said substance to be heated.