ABSTRACT
Consider the two columns of air AB and CD in Figure 32. These are of equal crosssectional area, height and temperature, so that the pressures at A and C are equal, as are those at B and D. Suppose the column AB is warmed: it will expand to AE, if the area remains constant, and although the pressure at A will remain unaltered, the pressure at B will have increased relative to that at D, and to equalize these air will flow from B to D. This transfer of air from column AB to CD will cause a drop in pressure at A and a rise at C, and air will now flow from C to A.
