Direction in which Storms may be premised that by the direction of a storm is meant, not the direction of the wind, but the path followed by the center of dis turbance. The direction in which their progressive motion takes place differs in differ ent parts of the world, being determined by the prevailing winds. See WuNns. Thus, about- half the storms of middle and northern Europe travel from the s.w. toward the n.e., and 19 out of every 20, at least, travel toward some point in the quadrant from the n.e. to the s.e. Observation shows that the longer axis of the storm is almost always coincident with the direction in which the storm appears to be moving at the time. Storms do not always proceed in the same uniform direction from day to day, and though the change which occurs in the directon of their progressive motion is generally small, yet occasionally it is very great. Thus, of the many interesting features peculiar to the storm which passed over Europe in the beginning of Dec., 1S68, none were Inure remarkable than the sudden changes of its progressive motion. It was first observed on the w. of Ireland, from which it advanced c. to Liverpool, then turnol s. through Wor cester and Oxford to Cherbourg in France; it thence retreated n. through Oxford to ' Shields, from which it proceeded e. to Copenhagen. By the time it arrived at Copen hagen its extent was only a fourth of what it had been the previous day, and the central depression half an inch less. Twelve hours later, the atmospheric equilibrium was restored, the storm having died out on reaching the Baltic sea. The storms of the Mcd iterranean follow a different course. Many of them proceed from the n. to the s., info cnced probably by the heated air rising from the Sahara; a considerable number procc«1 from the e., and pass to the westward over Greece and Italy to the Alps; v, bile very few are observed to travel in an easterly direction. By far the greater number of the storms of North America take their rise In the vast plain which lies immediately to the c. of the Rocky mountains, and thence advance in an eastern direction over the United States: some of them, crossing the Atlantic, burst on the western shores of But the relation of the American to the European storms is not yet established, nor will be till observation has collected more facts, and discussion has sifted their significance. If once the connection be fully esta Wished, the system of forecasting storms to European ports will become much more certain and complete than it is at present. The storms of the West Indies generally take their rise from near the region of calms, and tracing cut a parabolic course, proceed first toward the n.w., and then turn to the me. about 80° u. lat., many of them traversing the e. coasts of North America as far as Nova Scotia. South of the equator they follow an opposite course. Thus, in the south Atlantic and Indian ocean they first proceed toward the s.w., and then gradually curve round to the s.e. The hurricanes of Hindustan usually yuri-ue a parabolic path. first toversing the eastern coast toward Calcutta. and then turning to the n.w. up the valley of the Gauges. The typhoons of the Chinese seas resemble, in the course they take, the hurri canes of the West Indies. Observations are wanting horn other parts of the world to determine the course of storms.
Probably the course tracked out by storms is determined by the general system of winds which prevail, modified by the unequal distribution of laud water on the sur face of the globe. Facts seem at present to point to this general conclusion, viz., Norms follow the course of the «tmospheric current in which the condensation of the raper into the rain which accompanies them takes place.
Rate at which Storms travel.—if the position of the center of Storm I. on Nov. 2 be compared with its position on the 1st on the charts, it will be found to have traveled 420 m. in 24 hours, or at the rate of 174 in. an hour. Similarly Storm II. will be found to have traveled in the same time 400 na, or at the rate of 16 in. an hour. This is about the average rate of the progressive movement of European storms. Sometimes. how ever, it falls as low as 15 m. an hour, and sometimes increases to 30 in. an hour. Within the tropics the onward motion of storms sometimes rises to 40 m. an hour.
Relations of Temperature, Rain, and Cloud to Storms.—Tbe temperature ineret sc.s a few degrees 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 passed. In other words, the temperature rises as the barometer falls, and falls as the bar( rises When the brrometer has been falling for some time clouds begin to over: pit ad the sky, and rain to fall at intervals; and, as the central depression approaches, tl.e rain
becomes more general, heavy, and continuous. After the center of the storm hasp passed, or when the barometer has begun to rise. the rain becomes less heavy, falling more in showers than continuously; the clouds break up, and tine weather ushered in with cold breezes ultimately prevails. It should be here remarked that, if the temperature begins to rise soon and markedly after the storm has passed, a second storm may be expected shortly. The rainfall is.generally proportioned to the suddenness and extent of the barometric depression at the place where it falls.
Observations of thell'ind.—First as to the direction of the wind. If the winds in Storm II. on Nov. 2 be attentively examined they will be observed 'Si hiding round the area of low barometer in a circular manner, and in a direction. contrary to the motion of the hands of a watch, with—and be this particularly noted—a constant tendency to turn inward toward the center of lowest barometer. The wind in storms neither blows round the center of lowest pressure in circles, nor does it blow directly toward that center, but takes a direction nearly intermediate, approaching, however, nearer to the direction and course of the circular curves than of the radii to the center. The grt tour the force of the wind is at any place it will be observed to approach the more ut arly the direction here indicated. And where the direction of the wind differs to any mat( rial degree from this .general law, it is light, and consequently more under local which turn it front its course. Thus, the center of the storm being near Liverpool, the direction of the wind is s.w. at Paris, s. at Yarmouth, n.e. at Silloth, n. at Dublin, and n.w. at Cork—instead of s. at Paris, s e. at Yarmouth, n. at Silloth. n.w. at Dublin, w. at Cork, if it had bloWn directly to the area of lowest pressure; and W. at Paris. s. w. at Yarmouth. e. at Silloth, n.e. at Dublin, and n. at Cork, if it had circulated in the direction of the isobarometrie curves. Hence in this storm the winds eireulale routai the center of least pressure, or, to speak more accurately, the whole atmospheric s3 slum flows in upon the center in a spiral course. This rotatory peculiarity is common to all storms in the northern hemisphere that have yet been examined. In the southern ht mi sphere, a rotatory motion is also observed round the center of storms, but it takes place in a contrary direction, or in the direction of the motion of the hands of a watch, instead of contrary to that direction, as obtains n. of the equator Prof. Taylor has the merit of having first applied Dove's law of rotation to explain the direction of the rotation of storms round their center. This may be explained by referring to Storm II. on Nov. 2. On that morning, the pressure over England being much less than in surrounding countries, if the earth had been at rest, air-currents would have flowed from all directions to England, to fill up the deficiency, in straight lines. The earth, however, is not at rest, but revolves from w. to e. ; and as the velocity of rotation diminishes as the latitude increases, it is evident that the current which set out, say from Lyon to the n., would, on account of its greater initial velocity when it arrived at Paris. blow no longer directly to the n., but to a point a little to the e. of n.; in other words, it would no hanger be a s., but a s.w. wind. Again, sines the current from the n. of Scotland bad a less velocity than those parts of the earth's surface on which it advanced, it lagged behind, and consequently, by the time it arrived at Silloth in the n. of England, had changed from a'n. to a n.e. wind. Similarly the n.w. current changed to a n. the s.w. to a w., etc. Tire w.• and e. currents, since they continued in the same latittide, would have blown in the same direction, if they bad not been dis tu•bed by contiguous currents. Hence in a storm the whole system of winds rotates round the center. As a further confirmation of the truth of this theory, it is observed that when a high barometric pressure covers a limited space the wind is always observed gently whirling out of this area of high barometer, but in exactly opposite directions in both hemispheres from those assumed when it blows round and in upon an area of low pressure. It follows in the northern hemisphere that, as storms advance, the general veering of the wind at places lying u. of the path of their center is from n.e. by n. to w.; and at places s. of their center from n.e. by e. and s. to n.w., and conversely in the southern hemisphere.