An unusual mercury stick barometer with isothermal altitude scale Short and Mason Limited, London, first half of the 20th century The oak wall panel applied with cast-iron cistern and tube complete with Bunten air trap against twin silvered scales, the left annotated for ISOTHERMAL ALTITUDE FEET from -1000 to 0 to 24,000 and the right for INCHES from 12 to 32 and divided into twentieths, the right hand margin signed SHORT & MASON, LONDON and the top edge inscribed No. E.7641, (lacking mercury), the back panel 94cm (37ins) high. The firm of Short and Mason are recorded in Banfield, Edwin BAROMETER MAKERS & RETAILERS 1660-1900 as operating from 62 Hatton Garden, London 1873-75 then 40 Hatton Garden from 1876. They were leading makers of barographs and aneroid barometers well into the 20th century later merging with Taylor Instruments in 1969.It would appear that the lot is designed to demonstrate the non-linear relationship with regards to variance in air pressure versus altitude. The labelling of the altitude scale with the term 'isothermal' indicates that the scale is has no form of temperature compensation, in other words the altitude reading would only prove accurate if temperature remains the same.