METEOROLOGY. 



the necessary grounds. The foregoing chart of 

 Europe shews, from actual observations made at 

 upwards of 100 localities scattered over that 

 continent, the barometric pressure, and direction 

 and force of the wind, at 8 A.M. of the 2d of 

 November 1863, during part of the course of 

 two storms which passed over Europe at that 

 time. At the same hour of the previous day, the 

 centre of the first storm (I.) was near Christian- 

 sund, and that of the second was approaching the 

 west coast of Ireland. The isobarometric lines, or 

 lines shewing where, at the above hour, the height 

 of the barometer was the same, are given for every 

 two-tenths in the difference of the pressure. Hence, 

 where these lines approach near each other, or 

 crowd together, the difference of pressure, or the 

 atmospheric disturbance, was the greatest ; and 

 the least where they are most apart a distinction 

 of the utmost importance in determining where 

 the storm may be expected to rage in greatest 

 fury. The arrows shew the direction of the wind, 

 being represented flying with it The force of the 



wind is shewn (i) by plain arrows, >, which 



represent light and moderate winds ; (2) by arrows 

 feathered on one side only, > " '> , which represent 

 high winds ; (3) by arrows feathered on both sides, 

 ** >, which represent strong gales, storms, or 

 hurricanes. 



Form and Extent of Storm Areas. The cir- 

 cular isobarometric lines on the chart represent 

 very accurately the general shape storms assume. 

 The area of almost every storm is either circular 

 or slightly elliptical. The outline is occasionally 

 very irregular. The extent over which storms 

 spread themselves is very variable, being seldom 

 less than 600 miles in diameter, but often two or 

 three times that amount, or even more. 



Direction in which Storms advance. It may 

 be premised that by the direction of a storm is 

 meant, not the direction of the wind, but the 

 path followed by the centre of disturbance. The 

 direction in which this progressive motion takes 

 place differs in different parts of the world being 

 determined by the prevailing winds. Thus, 

 about half the storms of Middle and Northern 

 Europe travel from the south-west toward the 

 north-east, and 19 out of every 20, at least, travel 

 toward some point in the quadrant from the 

 north-east to the south-east. Observation shews 

 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. 

 The storms of the Mediterranean follow a differ- 

 ent course. Many of them proceed from the 

 north to the south, influenced probably by the 

 heated air rising from the Sahara. By far the 

 greater number of the storms of North America 

 take their rise in the vast plain which lies imme- 

 diately to the east 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 Europe. 

 But the relation of the American to the European 

 storms is not yet established. The storms of the 

 West Indies generally take their rise from near the 

 region of calms, and tracing out a parabolic course, 

 proceed first towards the north-west, and then 

 turn to the north-east about 30 N. lat, many of 

 them traversing the east coasts of North America 

 as far as Nova Scotia. South of the equator they 

 follow an opposite course The hurricanes of 



Hindustan usually pursue a parabolic path, first 

 traversing the eastern coast towards Calcutta, and 

 then turning to the north-west up the valley of 

 the Ganges. The typhoons of the Chinese seas 

 resemble, in the course they take, the hurricanes 

 of the West Indies. Observations are wanting 

 from other parts of the world to determine the 

 course of storms. 



Everywhere, the course tracked out by storms 

 is determined by the general system of winds 

 which prevail, modified by the unequal distribution 

 of land and water on the surface of the globe. 

 Facts seem at present to point to this general 

 conclusion, viz., Storms follow the course of tht 

 atmospheric current in which the condensation of 

 the vapour into the rain which accompanies them 

 takes place. 



The Rate at which Storms travel, varies from 

 15 or 17 miles an hour in Europe, to 30 or 40 

 miles in tropical countries. 



Relations of Temperature, Rain, and Cloud to 

 Storms. The temperature increases 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 barom- 

 eter rises. When the barometer has been falling 

 for some time, clouds begin to overspread the sky, 

 and rain to fall at intervals ; and as the central 

 depression approaches, the rain becomes more 

 general, heavy, and continuous. After the centre 

 of the storm has 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 fine 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 rain- 

 fall is generally proportioned to the suddenness 

 and extent of the barometric depression at the 

 place where it falls. 



Direction and Force of the Wind in Storms. 

 If the winds in Storm II. on the 2d November 

 be attentively examined, they will be observed 

 whirling 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 inwards towards the centre of lowest baro- 

 meter. The wind in storms neither blows round 

 the centre of lowest pressure in circles, nor does 

 it blow directly towards that centre, but takes a 

 direction nearly intermediate. In other words, 

 the whole atmospheric system flows in upon the 

 centre in a spiral course. This rotatory pecu- 

 liarity is common to all storms in the northern 

 hemisphere that have yet been examined. In the 

 southern hemisphere, a rotatory motion is also 

 observed round the centre of storms, but it takes 

 place in a contrary direction, or in the direction 

 of the motion of the hands of a watch. 



Professor Taylor has the merit of having first 

 applied Dove's law of rotation to explain the 

 direction of the rotation of storms round their 

 centre. The cause may be seen by referring 

 to Storm II. on the 2d November. 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 



