This apparatus was developed at CERN to measure magnetic permeability of steel samples. The samples are flat rings machined out of the steel to be measured. They are placed between the top and the bottom parts of the permeameter. Silver plated sliding contacts complete the excitation and the probe electrical circuits when the top half of the apparatus is closed down to the bottom part. Several copies of this instrument were produced and used to measure the magnetic permeability of the steels for ISR, SPS, LHC and many other magnets. See also photo 7708553X