Note 3 — Chapter III
Reading edition
The pressure of the wind supplied by the old horizontal bellows is regulated by the weights placed on top. The amount of this pressure is measured by a wind-gauge or anemometer invented by Christian Förmer about 1677. It is a bent glass tube, double U shaped, into which a little water is poured. On placing one end of it fitted with a socket into one of the holes in the wind-chest (in place of a pipe) and admitting the wind from the bellows the water is forced up the tube, and the difference between the level of the surface of the water in the two legs of the tube is measured in inches. Thus, we always talk of the pressure of wind in an organ as being so many inches.