The practical use of meteorological reports and weather-maps / Office of the chief signal officer, Division of telegrams and reports for the benefit of commerce.
- United States Army Signal Corps
- Date:
- 1871
Licence: Public Domain Mark
Credit: The practical use of meteorological reports and weather-maps / Office of the chief signal officer, Division of telegrams and reports for the benefit of commerce. Source: Wellcome Collection.
Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.
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![place the most rapidly, there the barometer will also fall the most rapidly, and thither the storm will be strongest drawn. Such storms naturally, therefore, move very rapidly up toward the lakes, and hang tenaciously over them, and move slowly away from them. In winter their course is eastward, in the early autumn northeastward. The temperature of the upper regions must decide whether rain or snow will attend these storms. Their advance is almost invariably heralded by an increase of temperature, due a]3par- ently to latent heat evolved by the condensation going on in the circumjacent and superior air and radiated downw^ard to the earth, and to the increased facility with which the saturated air on the surface absorbs the heat radiated by the earth. Following the increase of temperature the cirrus clouds are observed, which geographically precede the stratus and the rain. The lowest pressure is felt on the earth after the rain has begun to fall. Although often these storms pass over without rain, until they near the lake district or Eastern States, yet their first cause may be traced back to the changes going on in the southern and western limits of the United States; at least two such have been actually followed during the four or six days occupied in passing from the California coast to Kova Scotia, and many instances are recorded of those that have passed from Texas over Lakes Suj^erior and Huron. The strong winds of autumn on the lakes and in the North- western States with little or no rain are due to disturbances that move southeastward, and whose centers are generally in British America. 3d. Well-defined, though generally weak disturbances, have been observed to pass from the north to the south, or the north- west to the southeast, but these are probably rare in the United States and probably occur only in midwinter, when the north- east winds and high pressure in British America are excej)- tionally strong. Continuous snow, succeeded by cold, dry Aveather, characterize these storms, and such a one, on one occa- sion during the i)ast winter, after striking the coast of Alabama and turning eastward, ascended the Gulf Stream to the north- eastward, thus coursing around the area of high pressure that had then pushed southward over the lake region. 4th. The storms which are generally confined within the United States are the northers, tornadoes, and thunder-storms. The latter are generally spread over a very narrow space, so 3](https://iiif.wellcomecollection.org/image/b21070374_0043.jp2/full/800%2C/0/default.jpg)
