Ross Tendency Barometer

The Ross Tendency Barometer is mounted in an exquisitely crafted wood and curved-glass case. This barometer and its illustrations are a tribute to the famous Arctic 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.” This barometer consists of two liquid-filled mercury-free tubes. One tube is U-shaped open-ended and filled with a red fluid; and one closed thermometer tube is filled with a blue fluid. These two tubes are mounted parallel to each other for easy comparison.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 tall by 6.7 inches wide and weighs three pounds. This is an absolutely beautifully presented piece that will last for generations.