481. Wet gas meter. The stationary case, A, is filled with water up to above the center. The inner revolving drum is divided into four compartments, B, B, with inlets around the central pipe, a, which introduces the gas through one of the hollow journals of the drum. This pipe is turned up to admit the gas above the water, as indicated by the arrow near the center of the figure. As gas enters the compartments, B, B, one after another, it turns the drum in the direction of the arrow shown near its periphery, displacing the water from them. As the chambers pass over they fill with water again. The cubic contents of the compartments being known, and the number of the revolutions of the drum being registered by dial-work, the quantity of gas passing through the meter is registered.