Winter online exhibition
Accession number LIV.2000.138.147
A hygrometer measures the amount of humidity in the air. The atmosphere always carries a certain amount of water vapour, the proportion of which varies with temperature. The warmer the air the more moisture it will contain. As air becomes colder the water vapour in it condenses into moisture to produce dew or frost. In a mist or fog the air is completely saturated and this is called 100% humidity.
To measure the amount of humidity, hydroscopic material was used to move a pointer to indicate the amount of water vapour in the air. Common materials used were hair, whalebone, cat gut and impregnated paper.
The Lambrecht's polymeter is a normal hair hygrometer with a pointer passing over a scale reading 0 – 100% humidity. Above this is another scale in degrees celsius to be read in conjunction with the first scale.
A mercury thermometer (missing) reads the air temperature and the numerical difference between this and the value indicated by the hygrometer needle gives the temperature at which the onset of dew or fog will occur.
This Lambrecht's polymeter was made in about 1903 by Lambrecht, Gottingen and is now in the physical science collections at World Museum.
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