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  ABDNP201187a01.JPG - Assmann's Aspirated Psychrometer Richard Assmann developed his ventilated hygrometer in the late 1880s and early 1890s for measuring temperature and humidity, because of the variability shown by older sling hygrometers.  In the increasingly popular balloon flights in particular, the velocity of the local air relative to the balloon was almost zero and the traditional 'wet and dry' hygrometer was known to give poor results for humidity.   The provision of forced and controlled ventilation in Assman's instrument solved the air-flow problem, and the shielding from sunshine also solved the problem of the variable influence of solar radiation on temperature readings.  As a result, Assmann's psychrometer came to be considered as a standard instrument, used to calibrate other hygrometers. ABDNP:201187a  
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16 | Assmann's Aspirated Psychrometer

Richard Assmann developed his ventilated hygrometer in the late 1880s and early 1890s for measuring temperature and humidity, because of the variability shown by older sling hygrometers. In the increasingly popular balloon flights in particular, the velocity of the local air relative to the balloon was almost zero and the traditional 'wet and dry' hygrometer was known to give poor results for humidity.

The provision of forced and controlled ventilation in Assman's instrument solved the air-flow problem, and the shielding from sunshine also solved the problem of the variable influence of solar radiation on temperature readings. As a result, Assmann's psychrometer came to be considered as a standard instrument, used to calibrate other hygrometers.

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