Abstract: The invention relates to apparatus for measuring the index profile of an optical fiber preform that includes an outer envelope and a core. According to the invention, a deformable and transparent separation interface is provided between a deformable index isotropy medium and the outside surface of the envelope of the preform, said deformable separation interface adapting the deformable index isotropy medium to the outside surface of the envelope of the preform at least over an annular zone thereof, which zone corresponds to an optical measurement zone situated on the path of a light beam, said deformable and transparent interface, and inlet and outlet optical surfaces for the light beam all having an index close to the index of said medium.

Abstract: An assembly for permitting temperature measurements at a large number of locations within a vessel, which assembly has a spreader-reducer for compacting a significantly large number of thermocouple cables into a relatively small volume so as to permit passage through one or more vessel nozzles. The thermocouple cables each has a heat expansion portion as well as a seat, thereby permitting a series of horizontal arrays of thermocouple junctions positioned at different depths within the vessel.