| 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, mercury free 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 beautiful wood frame is made from European walnut with black trim and the
unit has colorful nautical flags along the right side. The thermometer measures in Fahrenheit and Celsius. The tendency dial
also measures air pressure in millibars. The frame is wood with an old
world type of finish and the parchment faceplate has nautical signal flags
printed along the side. It measures 19 inches
high by 7 inches wide. The unit comes fully assembled and includes a calibration
kit to adjust the unit for altitudes above sea level. User Manual
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