STORM-SIGNALS. 



099 



Those storms aro of cyclonical or rotary 

 UT. muting against tin.! hand* of a watch 

 in our hemisphere, and with the hands of a 

 w.it >-li in the southern hemisphere. Their 

 \vlority is such that they travel from the Mis- 

 sissippi to tii.- Connecticut River in about 

 twenty-four hours, and thence to St. John's, 

 Newfoundland, in nearly the same time, or 

 thirty-nix milvs an hour. These storms, after 

 crossing the Rocky Mountains, become elon- 

 gated from north to south, and move to the 

 east side-foremost. Within the limits of preva- 

 lent westerly winds, when storms advance 

 with very considerable rapidity, the direction 

 of progress is always from west to east. This 

 direction is not absolutely uniform, but has 

 been observed to vary from about due east to 

 N. 54 E. 



Great storms of rain and snow are accom- 

 panied by a depression of the barometer near 

 the centre of the storm, and a rise of the ba- 

 rometer near the margin ; but this rise is not 

 generally uniform along the entire margin. 



The depression of the barometer at the 

 centre of a storm sometimes amounts to more 

 than an inch below the mean height ; and the 

 rise along some portion of the margin some- 

 times amounts to more than an inch above the 

 mean height. 



Winter storms commence gradually, and 

 generally attain their greatest violence only 

 after a lapse of several days ; after a time their 

 violence gradually diminishes, and at length 

 they disappear entirely. This succession of 

 changes requires a period of several days, some- 

 times one or two weeks, and possibly even 

 longer. Sometimes all these changes are ex- 

 perienced over the same country ; that is, the 

 storm makes no progress from place to place. 

 More commonly, however, the storm travels 

 along the earth's surface ; and, although the 

 same storm may continue for one or two weeks, 

 or even longer, its Duration at any one place 

 may not exceed one' or two days. 



For several hundred miles on each side 

 of the centre of a violent storm the wind in- 

 clines inward toward the area of least pressure, 

 and at the same time circulates around the 

 centre La a direction contrary to the motion of 

 the hands of a watch. 



In Europe, as well as in the United States, 

 on the north side of a great storm, the preva- 

 lent winds are from the northeast, while on 

 the south side they are from the southwest. 



The force of the storm is proportional to 

 the magnitude and suddenness of the depres- 

 sion of the barometer ; but very near the centre 

 of a violent storm there is often a calm. 



On the borders of a storm, near the line 

 of maximum pressure, the wind has but little 

 force, and tends outward from the line of 

 greatest pressure. 



The wind uniformly tends from an area of 

 high barometer toward an area of low barom- 

 eter ; and this is probably the most important 

 law regulating tho movement of the wind. 



In a great storm the centre of the area 

 of high thermometer frequently doe not coin- 

 cide with that of tho area of low barometer, 

 or with tho centre of the area of rain and snow. 

 In the United States, on the northeast side of 

 a storm, at a distance of over five hundr. < 

 from the area of rain and snow, the thermom- 

 eter sometimes rises even twenty degrees above- 

 its mean height. 



The groat storm of March, 1859, for example, 

 in accordance with these laws, ran from West 

 era Texas, where it first struck our coast, in a 

 northeast direction to Lake Michigan, which it 

 reached in twenty-four hours, thence to the 

 Atlantic coast in another twenty-four hours, 

 and, finally, leaving the continent at St. John's, 

 Newfoundland, ninety-six hours after its first 

 announcement. Hero was a regular movement 

 about as rapid as a railroad train, and as easily 

 kept under supervision. The storm of Feb- 

 ruary 22, 1871, was anticipated, by cautionary 

 telegrams from the Signal-Office for four days, 

 to all cities eastward from San Francisco 

 (where it first appeared), to the city of Oswego 

 in New York. 



Experience of the most accomplished navi- 

 gators, meteorologists, and practical observers, 

 has established, moreover, certain unquestion- 

 able premonitions of storms. 



These have been given by various writers on 

 meteorology as follows: 



A premonition of an approaching gale is af- 

 forded to seaport towns by the agitation of 

 the ocean and the disturbance of its slimy bed. 

 The muddy appearance of the water in the 

 sea, in anchoring depths, during violent storms, 

 sometimes precedes the storm, being caused 

 by heavy undulations affecting the bottom of 

 the sea. This effect was remarkable around 

 the Bermuda Islands in September, 1839, a 

 day before the actual arrival of the tempest. 



Clouds are of the utmost utility in for tell- 

 ing weather, especially the cirrus, cirro-stratus, 

 and cumulo-stratus. 



The cirrus, called by sailors "cat's tail," 

 and sometimes by others the "curl cloud," is 

 made up of wavy parallel or diverging fibres, 

 or slender filaments like white lines pencilled 

 on tho blue sky. It is probably composed of 

 minute snow-flakes or ice-crystals. Its move- 

 ment is a fine index of the great atmospheric 

 currents, and it is thus a valuable prognostic 

 of stormy weather. It doubtless often reaches 

 a height of ten miles above the earth. When 

 the fine threads of the cirrus appear blown or 

 brushed backward at one end, as if by a wind 

 prevailing in these lofty regions, the wind on 

 the surface will sooner or later veer round to 

 that point. 



The cirro-stratus, partaking of the form of 

 both the cirrus and stratus, Buchan says, "is 

 markedly a precursor of storms ; and, from its 

 greater or less abundance and permanence, it 

 gives some indication of the tune when the 

 storm may be expected." 



The cumulo-stratus is distinctly formed just 



