Comparative thermometer

Bryson's 'Comparative Thermometer' gives the temperature in degrees Celcius (left), Fahrenheit (centre) and Reaumur (right). Down each side of the instrument is a list of important towns all over the world, with corresponding average midday shade temperatures for winter (W), summer (S), or yearly average (Y). It was designed by the Geographer-in-Ordinary to the Queen, Alexander Keith Johnston (1804-71), Hon. Secretary and founder member of the Scottish Meteorological Society, who was in partnership with his brother as W. & A.K. Johnston, famous for their maps and globes.

This spirit-in-glass thermometer mounted on a ceramic scale is marked at the top: 'BRYSON'S / NEW / Comparative / Thermometer / Arranged by / A.K. Johnston. F.R.S.E.'. The scale in degrees centigrade and Reaumur is marked from -17 to 37 degrees C, and -13 to 29 degrees R. The scale shows winter and summer extremes, and temperature means, for different parts of the globe.

James Mackay Bryson (1824-94), from an Edinburgh dynasty of instrument makers and scientists, appears to have been interested in the applications of thermometers for special purposes; but this particular example was probably a one-off special commission, and is more a curiosity than a 'scientific instrument'.

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