Abstract: The present invention relates to an instrument for measuring the variations in intensity of a beam of X-rays scattered by liquid or amorphous solid materials, which comprises: a goniometric head carrying said material and mounted rotationally movable, a position sensitive proportional detector mounted movable along a radial supporting arm, with a rotational motion which is coaxial to the motion of said goniometric head, and having an angular amplitude twice that of the angular change of location of said head, and a monochromator situated on the X-ray beam. Such an instrument is specially designed for liquid or amorphous solid materials, which only scatter an X-ray beam with a very low intensity. The monochromator or said instrument is located on the path of the beam of X-rays scattered by said liquid or amorphous solid material, after the latter and before said position sensitive proportional detector.

Abstract: Selective optical resonator comprising at least two mirrors and a selective means disposed between two of these mirrors, said means being constituted by:an at least partial linear polarization means for the light in a direction P,a first birefringent plate having two neutral lines, one forming an angle .alpha..sub.1 =0 with direction P,an optically active substance having a birefringence with dispersion and which rotates the light polarization direction by an angle .theta. dependent on the wavelength of the .lambda. light,a second plate which is identical to the first having two neutral lines, one forming the angle .alpha..sub.2 =.theta. with the direction P, whereby the resonator is then selective for said wavelength .lambda..