Page:Collier's New Encyclopedia v. 09.djvu/140

LEFT STORM 106 STORM STORM, a violent commotion or dis- turbance of the atmosphere, producing or attended by wind, rain, snow, hail, or thunder and lightning; a tempest; often applied to a heavy fall of rain, snow, etc., without a high wind. There is, perhaps, no question in science in which there was long so large an admixture of specula- tion with fact as in the attempts made to reduce the phenomena of storms under general laws; the reason being that me- teorological observatories were too few in number and too wide apart to repre- sent the barometer pressure, the general course of the winds, and the rainfall, without drawing largely on conjecture. The extent over which storms spread is very variable, being seldom less than 600 miles in diameter, but often two or three times greater, and more rarely even five times that amount. More than the whole of Europe is sometimes over- spread by a single storm at one time. The prime difference between storms or cyclones and tornados is that the breadth of the space traversed by the latter is, as compared with that of storms, al- ways quite insignificant. The area of storms is not constant from day to day, but varies in size, sometimes expanding and sometimes contracting; and it is worthy of remark that when a storm contracts in area the central depression gives signs of filling up, and the storm of dying out. On the other hand, when it increases in extent the central de- pression becomes deeper, the storm in- creases in violence, and occasionally is broken up into two or even more depres- sions, which become separate storms, with the wind circling round each. This occurs frequently with summer thunder- storms. Direction in Which Storms Advance. — The direction in which their progressive motion takes place differs in different parts of the world — being perhaps de- termined by the prevailing winds. Thus, about half the storms of middle and northern Europe travel from the S. W. toward the N. E., and about 19 out of every 20 travel toward some point in the quadrant lying between the N. E. and the S. E. Storms rarely travel toward a W. point; in some of the instances which have been noted the W. course has been arrested at Norway, Denmark, the North Sea, or the British Islands, but such W. course is temporary, the E, course being aft«erward resumed. Some of the most violent E. storms fall under this head. Storms do not always pro- ceed in the same uniform direction from day to day, and, though the change which occurs in the direction of their progres- sive motion is generally small, yet oc- casionally it is very great. The storms of the Mediterranean fol- low a different course. While a number take the general E. course of European storms, a larger number originate in the gulfs of Lyons and Genoa, and pur- sue devious courses over this N. exten- sion of the Mediterranean, till they die out; several advance from Turkey and Greece toward the Alps; and others, com- paratively few, advance in an E. course toward the Levant. By far the greater number of the storms of North America take their rise in the vast plain which lies to the E. of the Rocky Mountains, and thence advance in an E. direction over the United States, their course being largely determined by the Great Lakes; some of them cross the Atlantic, and burst on the W. shores of Europe. But the connection of the American with the European storms is not even yet well established. The storms of the West Indies generally take their rise some- where N. of the region of calms, and, tracing out a parabolic course, proceed first toward the W. N. W., and then turn to the N. E, about lat. 30° N., not a few traversing the E. coasts of North America as far as Nova Scotia. South of the equator they follow an opposite course. Thus, in the Indian Ocean they first proceed toward the S. W., and then gradually curve round to the S. E. The hurricanes of India usually pursue a parabolic path, first traversing the E. coast toward Calcutta, and then turning to the N. W. up the valley of the Ganges. The typhoons of the Chinese Sea resem- ble, in the course they take, the hurri- canes of the West Indies. Rate at Which Storms Travel. — The average rate of the progressive move- ment of European storms is about I6V2 miles per hour. From an examination of extensive series of storms Professor Loomis has shown that the average rates of progress of storm centers are in miles per hour 28 for the United States, 18 for the middle latitudes of the Atlantic Ocean, 17 for Europe, 15 for the West Indies, and 9 for the Bay of Bengal and China Sea. On Jan. 7-8, 1877, a storm traveled in 24 hours from Indianola, Tex., to Eastport, Me. — 1,782 miles, or 78 miles an hour. On the other hand, the rate of progress is, particularly in the tropics, sometimes so slow as to be virtually stationary; and, as already stated, they occasionally recurve on their paths. Relations of Temperature, Rain, and Cloud to Storms. — Temperature increases at places toward which and over which the front part of the storm is advancing, and falls at those places over which the front part of the storm has already Dassed. In other words, the temperature