|a.||A graphical representation, based on the latest information, of the relative proportions, at various elevations, of all the important gases of the atmosphere.|
|b.||A discussion of the importance of dust particles in the air to the widely different phenomena of sky light, by which we get indirect illumination, and the condensation that precedes and leads to precipitation.|
|c.||A discussion, with the aid of an elaborate series of diagrams based on extensive cloud observations, of the movements of the air at various elevations in cyclones and anticyclones.|
|d.||A discussion, illustrated with diagrams, of the vertical distribution of temperature during different seasons and different weather conditions.|
|e.||An account, both descriptive and explanatory, of the isothermal layer, which, as sounding balloons have shown, is always and everywhere present.|
|f.||A chapter on weather forecasting, illustrated by over thirty typical charts of the weather. A study of this chapter should enable the layman, with the aid of a daily weather map, to make a good forecast of the coming, weather for two or three days ahead.|
Weather and Climate. --Many of the phenomena of which we shall treat may be broadly classified under the terms Weather and Climate. Weather expresses the conditions of the air at a definite time. One may properly speak of the weather of yesterday, but not of the climate, which is determined by taking the average of all the meteorological observations for a period of time great enough to eliminate the irregularities due to the variations of the weather from day to day. The science of weather, or dynamic meteorology, will receive the larger share of our attention; it treats of the generation and the movement of storms, the production of clouds and rain, the heating of the air, and the general circulation of the atmosphere.
J. HANN'S "Lehrbuch der Meteorologie," 1st ed., Leipzig, 1901; 2d ed., Leipzig, 1906, is the most complete digest of current knowledge and opinion in most departments of meteorology. The first edition is rich in bibliographical references; the second is reduced in size, for use as a text- book. Teachers and advanced students who can read German should have access to both. There is no English translation.