Abstract: A spectrograph for an extended spectral field having an inlet slot for defining a source of light to be analyzed and a dispersive system constituted by a concave holographic grating which has recording points with coordinates in relation with the coordinates of the light source to be analyzed to produce for each of respective bands of wavelengths, which in total cover the entire range of wavelengths of the spectral field to be analyzed, tangential focal lines for different wavelengths which are disposed in the same plane. The concave holographic grating is rotatable around an axis passing through the center of the grating and perpendicular to a plane passing through the center of the inlet slot so that the respective partial plane diffraction spectra are successively formed in the same plane when rotating the grating around its axis.

Abstract: A spectrograph for use in analyzing an extended spectral field comprising a dispersive system consisting solely of one or more concave holographic gratings, each grating being specified so that the diffraction spectrum is formed in a plane. Where a plurality of gratings are provided they are formed on a common concave support and are specified so that the planes of the diffraction spectra formed thereby are offset and in total cover the wavelengths of the total spectral field.

Abstract: A furnace for melting metal by the Joule effect to enable extraction of gases contained in the metal comprising a hollow tubular body which constitutes a heater resistor clamped between two electrodes, and a separate crucible for the metal which is supported within the tubular body and out of direct contact with the electrodes.

Abstract: A monochromator having a concave holographic grating which is turnable in rotation and provided with an inlet slot parallel to the lines of the grating for incident light and an outlet slot also parallel to the lines of the grating, the inlet and outlet slots being disposed on opposite sides of a diametrial median plane P of the grating extending perpendicular to the lines of the grating and passing through the center of the grating. The bisector of the angle A, formed by two lines connecting the center of each slot to the center of the grating is contained in the plane P, the slots being additionally disposed such that the projection .alpha. of the angle A on the plane P is .ltoreq. 3.degree. and the projection .beta. of the angle A on the plane P' containing the bisector and perpendicular to the plane P is .ltoreq. 15.degree..

Abstract: A monochromator having a fixed inlet slot, a holographic grating carried on a concave turnable support, and a fixed outlet slot, the support surface of the holographic grating being a concave portion of a toroidal surface, taken at the outer periphery of the toroid, and symmetrically disposed with respect to the equatorial plane of the toroid, the equatorial plane also containing the point sources for recording the holographic grating.