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the recurrent average conditions that we may expect, in successive seasons, repeated year after year, which we call climate."

The above statement gives an idea of the scope and method of treatment of the subject. There are a few points, however, which deserve more particular mention. In chapter III., the distribution over the earth of the insolation, or radiant energy received by the earth, is discussed, and by means of a very ingenious diagram, the amount of insolation for all latitudes for each month of the year is graphically shown. A detailed discussion of the various processes of absorption, conduction, radiation, and convection, by means of which the atmosphere gains and loses heat, is given. In the course of this the author takes exception to the statement, so common in most physical geographies, in which the atmosphere is "compared to a trap which allowed sunshine to enter easily to the earth's surface, but prevented the free exit of radiation from the earth." In reality, the coarse-waved radiation from the earth passes out readily without great absorption, either by the clear air or the water-vapor, which has been proved to be as poor an absorber as pure dry air.

Again, the exact processes, by which convectional circulation is set up, are clearly brought out, and the incorrectness of such loose statements, as "the air is heated and rises, and the cold air rushes in from either side to fill the vacuum thus formed," is emphasized.

A general review of the distribution of pressures and the circulation of the winds shows the student two particulars, in which the expected arrangement of pressures and motions according to the theory of convection, as applied to the origin of winds, are contradicted by the facts. The polar pressures are high, not low, the highest pressures occur around the tropics, where intermediate pressures were expected, and the winds do not follow the gradients, but are systematically deflected. Either the convection theory is fundamentally wrong as an explanation for the winds, or it needs to be supplemented by some factors up to this time unconsidered. This fact the author brings clearly to the mind of the pupil, who is then led to see that, perhaps, the oblique course of the winds may account for the distribution of pressures at the poles and the tropics. The cause of the oblique course is found in the deflecting influence of the earth's rotation. It is proportionate to the velocity of motion, and increases from zero at the equator to a maximum value at either pole, but it does not depend upon the direction in which the body is mov-