The Ross Tendency Barometer is mounted in an exquisitely wood and curved glass case. A tribute to the famous Artic and Antarctic explorer James Clark Ross (1800 -1862) discoverer of the magnetic North Pole. His ship, the Erebus, is pictured at the top of the instrument and a map of the Antarctic is pictured below.
The Tendency Barometer was patented on December 23, 1818 by Alexander Adie. It was used by Ross on his expeditions. He is quoted in his diary as saying " the advantage of the tendency barometer to a mercury barometer is as big as having a mercury barometer to having no barometer at all." It consists of two liquid filled tubes. One tube in a U-shaped which is open ended and filled with a red fluid; and one closed thermometer tube filled with a blue fluid, mounted parallel to each other.
When the fluid levels are the same, the weather is changing.
When the red fluid level is below the blue fluid level, the weather is fair (high pressure pushes the red fluid down in the tube).
When the red fluid level is above the blue, stormy weather is predicted (low pressure allows the red fluid to move up the tube).
The thermometer measures in both Celsius and Fahrenheit and the barometer measures in millibars/ hPa. The overall instrument measures 20 inches high by 6.7 inches wide and weighs 3 pounds. An absolutely beautiful presentation piece that will last for generations.
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