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Athermo-hygrograph orhygrothermograph is achart recorder that measures and records bothtemperature andhumidity (ordew point). Similar devices that record only one parameter are athermograph for temperature andhygrograph for humidity.
Thermographs where the variations are recorded usingphotography were described by several scientists as early as 1845, includingFrancis Ronalds who was Honorary Director of theKew Observatory. An updated model of the initial machine was deployed across the national observational network set up by the new UKMet Office in 1867 and coordinated by Kew Observatory.[1][2] These instruments then saw extended use around the world.
An alternative thermograph configuration has a pen that records temperature on a revolving cylinder. The pen is at the end of a lever that is controlled by a bi-metal strip of temperature-sensitive metal which bends as the temperature changes. A human hair bundle can be used for humidity in such machines.
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