. Handbook of nature-study for teachers and parents, based on the Cornell nature-study leaflets. Nature study. Snow crystal. Photomicrograph by W. A. Bentley. Weather Maps A weather map is a sort of flashlight photograph of a section of the bottom of one or more of these great rivers of air. It brings into view the whole meteorological situation over a large territory at a given instant of time; and, while a single map con- veys no indication of the movements continually taking place in the atmosphere, a series of maps, like a moving picture, shows not only the whirling eddies, the hurrying cl
. Handbook of nature-study for teachers and parents, based on the Cornell nature-study leaflets. Nature study. Snow crystal. Photomicrograph by W. A. Bentley. Weather Maps A weather map is a sort of flashlight photograph of a section of the bottom of one or more of these great rivers of air. It brings into view the whole meteorological situation over a large territory at a given instant of time; and, while a single map con- veys no indication of the movements continually taking place in the atmosphere, a series of maps, like a moving picture, shows not only the whirling eddies, the hurrying clouds and the fast-moving winds, but the ceaseless on-flow of the great river of air in which they float. Our present knowledge of the movements of the atmosphere has been gained chiefly from a study of weather maps; they form the basis of the modern system of weather forecasting, and their careful study is essential to any adequate understanding of the problems presented by the atmosphere. (See pages 884-885.) The Principles of Weather Forecasting The forecasting of the weather has been made possible by the electric telegraph. It is based upon a perfectly simple, rational process constantly employed in everyday afiiairs. We go to a railway station and ask the operator about a certain train. He tells us that it will arrive in an hour. We accept his statement without question, because we are confident that he knows the speed at which the train is ap- proaching, a few clicks of his telegraph instru- ment has told him just where it is and the time it will arrive, barring accidents, is a simple calcula- tion. Information of coming weather changes are obtained in a similar manner. Although storms do not run on steel rails like a train, nevertheless their movements may be foreseen with a reasonable degree of accuracy, depending chiefly upon the size of the territory from which tele- graphic reports are received and the experience and skill of the forecaster. As a rule, the larger the
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