1820 Daniell Hygrometer

Invented in 1820 by John Frederic Daniell, an English natural philosopher. This unique and scarce Hygrometer consists of a glass ball partially-filled with liquid ether (likely sulfuric acid); connected via a long, thin glass tube from which air been evacuated, to a second ball which is then covered in muslin . When ether is placed on the muslin-covered ball, the evaporation chill will cause the ether vapor inside to condense, forming a visible dew-point on the opposite balls' surface. 

A wooden stand and base houses a paper thermometer, graduated every degree and mounted on an outer white porcelain thermometer which is numbered every ten degrees, ranging from -20 to +50 degrees Centigrade.

Similar Model Featured in The Smithsonian (National Museum of American History).

Diameter: 4.5"

Height: 13"

Glass Width: 7.5"

Weight: 12 oz.