The amount of energy required to change the lapse rate of an atmospheric layer from one value to another is given by Q = (γ2γ1) QI where 
is the energy required to change the layer of thickness zo and mean density ρm from isothermal to dry adiabatic conditions. The height to which a given amount of effective insolation will establish an adiabatic lapse rate may be found by means of this formula, given the temperature- height curve in the early morning, and from this the expected maximum temperature may be evaluated.

Of the total solar radiation received at the ground, some is reflected, some goes to heat the earth's surface, some is sent back as long-wave radiation, some is used in evaporation, and the remainder is effective in heating the lower layers of the atmosphere. Estimates are made of the amounts used in the first four ways. These amounts subtracted from the average insolation received on clear days leave the effective insolation for changing the lapse rate near the ground.

The effective insolation at Chicago is arrived at in this way. Using these values, the maximum temperature was computed for several days when advective change was expected to be slight. The agreement with observation was found to be excellent.

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*On leave from U. S. Weather Bureau. This paper was presented at a staff meeting, U. S. Weather Bureau, Washington, D.C., April, 1940 and at the Cambridge Seminar, Feb., 1941.