One of the most precise types of wet-dry bulb psychrometer was invented in the late 19th century by Adolph Richard A�mann ( 1845 1918 ); in English-language references the device is usually spelled " Assmann psychrometer . " In this device, each thermometer is suspended within a vertical tube of polished metal, and that tube is in turn suspended within a second metal tube of slightly larger diameter; these double tubes serve to isolate the thermometers from radiant heating.
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