Page:Popular Science Monthly Volume 40.djvu/425

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December 20, 1836 — concerning wliicli, it occurring on one of tlie term days which Sir John Herschel had suggested as days for a general system of observations, he was able to collect data from all parts of the United States and some stations in Canada. His discussion of this storm, in a paper read before the American Philosophical Society in March, 1840, was. Prof. Newton says, " probably more complete than that of any previous one, and the methods which he employed were better fitted to elicit the truth than any earlier methods. . . . The results which he was able to secure did not sustain either of the two rival theories, but rather tended to prove some features in each of them." The studies were continued with the examination of the track of a second tornado in February, 1842, which proved to be a part of a general storm, and of another great storm that occurred in the same month. The paper embodying the results of these observations, which was read at the centennial meeting of the American Philo- sophical Society, in May, ]843, is remarkable for ha\dng intro- duced a new method of investigation. The delineations of storms previous to the composition of this paper had attempted no more than to indicate the progress of the center of minimum pressure by lines drawn from point to point, to which a few lines were added to show certain facts about the movements of the air. " In the discussion of the storms of 1842, instead of the line of minimum depression of the barometer, Prof. Loomis drew on the map a series of lines of equal barometric pressure, or rather of equal deviations from the normal average pressure for each place. A series of maps representing the storm at successive intervals of twelve hours were thus constructed, upon each of which was drawn a line through all places where the barometer stood at its normal or average height. A second line was drawn through all places where the barometer stood two tenths of an inch below the normal," etc. ; and also for places where the ba- rometer stood above its normal height. " The deviations of the barometric pressure from the normal were thus made prominent, and all other phenomena of the storm were regarded as related to those barometric lines. A series of colors represented respective- ly the places where the sky was clear, where the sky was over- cast, and where rain or snow was falling. A series of lines repre- sented the places at which the temperature was at the normal, or was 10°, 20°, or 30° above the normal or below the normal. Ar- rows of proper direction and length represented the direction and intensity of the winds at the different stations. These successive maps for the three or four days of the storm furnished to the eye all its phenomena in a simple and most effective manner." The introduction of this method, which is the prototype, still but lit- tle improved upon, of the weather charts now in general use, is

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