The isothermal surfaces are coaxial cylinders.
I by the whole area B"DZ'VO under the isothermal 9"D and the adiabatic DZ', bounded by the axes of pressure and volume.
The isothermal lines, in fact, suggest that in the vast area of the Pacific something corresponding to the " planetary circulation " is established, further investigation of which may be of extreme value in relation to current inquiries concerning the upper air.
It is often impossible to observe the pressure-coefficient dp/de directly, but it may be deduced from the isothermal compressibility by means of the geometrically obvious relation, BE = (BEÆC) XEC. The ratio BEÆC of the diminution of pressure to the increase of volume at constant temperature, or - dp/dv, is readily observed.
The difference 90-E is represented by the area 9"DdO to the left of the isometric Dd under the isothermal B"D.