RAINFALL AND CLIMATE.
The Distribution of Rainfall over the Land. By Andrew J. Herbertson. (J. Murray. 5s.)—Only the practical meteorologist, we suppose, can quite appreciate the years of patient and intel- ligent labour that must have gone to the preparation of Dr. Herbertson's useful and lucid monograph on the distribution of rainfall, which is now published under the auspices of the Royal Geographical Society. Dr. Herbertson, in a short but eminently satisfactory introduction to his work, points out the importance of the water which is always in the air, alike to the meteoro- logical theorist and to the practical farmer. He says :— "The moisture in the atmosphere has never been so thoroughly studied as some other elements of meteorology, notably temperature and pressure. Yet it plays no small part in the economy of the world. Water is the great vaiiable in the atmosphere. Unlike the two chief constituents, nitrogen and oxygen, it is found not merely in different quantities, but also in different physical states in different places, and, indeed, at the same place at different times. It is a sort of life-blood of the atmosphere, penetrating all parts of it. As vapour, it lessens the density of the atmosphere; as cloud, it absorbs the solar rays, and thus diffuses the sun's heat through the upper atmosphere. instead of allowing it to pass on to the earth's surface ; as rain, it clears the air of dust and other impurities. Its rapid and pro- tean changes under the influence of varying temperatures involve great transformations of energy, and are the main source of the enormous power displayed in all the great commotions in the atmosphere. It has also a conservative influence in diminishing the difference of temperature between day and night by the heat absorbed and given out in its alternate evaporation and con- densation, and by the shielding action of clouds to solar and terrestrial radiation."
It will be an inspiring thing to think of all these services the next time that our plans are deranged by a wet day, and in due time we shall no doubt learn to suffer waterproofs gladly. The study of rainfall in a really scientific way is scarcely twenty years old,—it was in 1852, as Dr. Herbertson points out, that the first good "annual rainfall map of the world" was published. Yet its importance can hardly be overrated, since it is by the study of rainfall alone that the variation of the water contained in the atmosphere can be investigated, and ultimately, perhaps, predicted. Meteorologists have recognised this, and now there are more than tweaty-five thousand stations where the rainfall is watched by skilled observers. Dr. Herbertson has set himself to co ordinate their reports, and has adopted the graphic plan of presenting a map of the world for each month in the year, coloured and contoured in accordance with rainfall, supplemented by a map of the mean annual rainfall, and a table of the monthly distribution of rain at a number of selected stations. We are full of admiration for the truly scientific and accurate manner in which Dr. Herbertson has compressed his immense study into these simple and easily comprehensible maps. We cannot deal at length with the results of his work, which should long remain a standard authority, but we may conclude this notice by quoting his interesting deductions :—
" First of all there are seven well-marked bands of high and low rainfall girdling the earth. These are
(1) Sub-equatorial wet belt. (2) and (3) Sub-tropical dry belts. (4) and (2) Temperate wet belts. (6) and (7) Polar dry caps.
Secondly, these hyetal belts move north and south with the sun. Thirdly, in equatorial regions there are two wet and two dry seasons every year; and fourthly, most rain fails when the sun is highest at noon, except on the west coast of temperate lands."
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