A pressure is often stated as being equal to so many inches of water. If the height of water were 1 1/2 in., the expression would mean a pressure equal to that caused by a column of water l 1/2 in. high, or, in other words, the weight of such a column. On the square foot this will mean a pressure of 7.794 lb.; on the square inch, 1/141 of this, or .054 lb . The higher pressures are usually measured by a Bourdon or other pressure-gauge; the light pressures are ascertained by inserting a tube and measuring how many inches of water in the tube are required to balance the pressure - thus the term, a pressure equal to so many inches of water.