mid-19th century, English, constructed of two mahogany frames hinged to the mahogany base, lower frame black reflecting glass raises to 18 degrees to the horizontal, held by a catch to the upper leaf which set that to 52 degrees, upper frame set with glass panel set with 15 selenite sections, measuring the direction of polarization of sunlight in the atmosphere, hour given by the number closest to the selenite showing maximum colour, upper frame also bearing maker’s plaque ‘Darker Lambeth’, base 11cm x 14cm, complete with a nicol prism polarizer in brass case. Note: This is the only example of this model we are aware of outside a major museum; provenance, purchased from Tesseract in 2011. For further information see Alan A Mills, Polarization of Light from the Sky and its Application to Timetelling, Bulletin of the Scientific Instrument Society No. 33 (1992)