Dasymeter

Dasymeter at standard pressure
Dasymeter at reduced pressure
Historical drawing of a dasymeter (in German: "Fig. 109. Baroscope. (Apparatus for proving the buoyancy of air)")

A dasymeter was meant initially as a device to demonstrate the buoyant effect of gases like air (as shown in the adjacent pictures). A dasymeter which allows weighing acts as a densimeter used to measure the density of gases.