Source : Webster's Revised Unabridged Dictionary (1913)

Dasymeter \Da*sym"e*ter\, n. [Gr. ? rough, thick + -meter.]
   (Physics)
   An instrument for testing the density of gases, consisting of
   a thin glass globe, which is weighed in the gas or gases, and
   then in an atmosphere of known density.

Source : WordNet®

dasymeter
     n : densimeter consisting of a thin glass globe that is weighed
         in a gas to determine its density