Dated 1827-1845. From Scientific apparatus, musical instruments and telegraph equipment, [1834-1875].

Dew point hygrometer developed by John Frederic Daniell (1790-1845), chemist and Professor at King's College London, to measure humidity.  Ether is poured over the muslin-covered bulb.  The ether evaporates, cooling the liquid inside the tube, causing water vapour from the ambient air to condense on the black surface of the second bulb.  The temperature inside the black bulb is read off the integral thermometer and compared with the temperature of the ambient air in order to determine the relative humidity.  Consists of glass tubes on a wooden stand. Possibly used by Wheatstone in teaching demonstrations. [See K/PP107/5/102 and 103.]