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Magnetograph. This apparatus was erected by the French physicist Eleuthere Mascart (1837-1908) in Mountsouris, Paris, France. It was designed to measure the variations in the local magnetic field, with a system of light beams and mirrors used to co-ordinate the different parts of the apparatus. At lower left is a magnetic balance. At centre left are temperature and humidity monitors. Three solenoids (marked 'H') help track the time. The results are recorded by the apparatus at centre right. Artwork from the eighth volume (second period of 1891) of the French popular science weekly 'La Science Illustree'.
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