754 



STORMS 



a south-west wind. Again, since the current from 

 die north of Scotland hail a less velocity tlnin those 

 parts of the earth's surface mi which it advanced, 

 it lagged behind, ami consequently )>v tin- linn' il 

 arrived at Silloth in tlie nortli of Boglaad liail 

 changed from a north to a north i-.i-i wind. Simi 

 hiily the north- west current changed to a ninth, 

 tin- south-west to a went, &c. The west and east 

 currents, since they continued in the name latitude, 

 would have blown in the same direction, if they 

 had not been disturbed by contiguous currents. 

 Hence in a storm the whole system of winds appears 

 to rotate round the centre. As a further con- 

 firmation of this theory, it is observed that when 

 a high 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 ii|>oii an area of low pressure. 

 It follows in the northern hemisphere that as 

 storms advance the general veering of the wind at 

 places lying north of the path of their centre is 

 from north-east by north to west, and at places 

 south of their centre from north-east by east and 

 south to north-west, and conversely in the southern 

 hemisphere. 



Force of the Wind. The rule is simple, and 

 without exception viz. the wind blows from a 

 high to a low barometer with a force pro- 

 portioned to the barometric gradient or to the 

 difference of the barometric pressures reduced to 

 sea-level. Hence where the isobaric lines crowd 

 together the violence of the storm is most felt, 

 and where they are far asunder the winds are 

 moderate, light, or nil. We thus see the import- 

 ance of observations from a distance in forecasting 

 the weather. To take an illustration : the import- 

 ance of observations from Norway and Sweden to 

 all seaports on the east coast of Britain cannot 

 be overestimated, for if the pressure lie high in 

 Norway and low in the North Sea or in the south 

 of Great Britain violent easterly gales will sweep 

 down on Scotland, and, unless foreseen and pro- 

 vided against, strew the coast with wrecks ; 

 whereas if the pressures be nearly equal little 

 danger need be apprehended, even though the 

 barometer be low in Britain. As the wind nears 

 the centre of the storm it gradually abates, till on 

 reaching the centre a lull or calm takes place a 

 peculiarity more uniformly noted as regards tropj- 

 cal storms. Calms and light winds also prevail 

 along the ridge of highest barometer, or the region 

 where the pressure is greatest, and on receding 

 from which the pressure diminishes on each side. 

 This arrangement of the pressure is accompanied 

 with fine weather and the ' pet ' days of winter. It 

 may not inaptly lie compared to the watershed in 

 physical geography, since from it the wind Hows 

 away on either hand towards the places where 

 pressure is less. 



The progressive motion of storms, which may 

 vary from zero to 78 miles an hour, measures the 

 time taken in passing from one place to another, 

 but it gives no indication of the violence of the 

 storm. This is determined by tin- velocity of the 

 wind round and inwards U|xin the centre of the 

 storm, which in Europe and America frequently 

 amounts to 60 or 80 miles an hour continuously for 

 Home time. In intermittent gusto a speed of 120 

 miles an hour has been several times oltserved in 

 Britain a velocity which is jierhaps sometimes 

 surpassed by storms within the tropics. On the 

 top of Ben Nevis higher velocities, rising to up- 

 wards of 150 miles, are of not infrequent occurrence. 



I'niue of Cyclones. Dove, who did HO much in 

 tliis department of meteorology, held the view that 

 cyclones are formed when two great atmospheric 

 currents, called polar and equatorial, flow side by 



-idc, storms being the eddies, as it were, formed 

 along the line of junction. It is to be kept in 

 mind that the qualities of the atmosphere in the 

 front jKiition of a cyclone are quite different from 

 in the rear the former U'ing warm and 

 moist, while the latter are cold and dry. The 

 conclusion is inevitable that the apparent rotation 

 of winds in storm* is -imply a circulatory move- 

 ment maintained between two currents, and that 

 no mass of the same air makes the complete circuit 

 of the cyclone. This feature of storms will, if 

 rightly apprehended, play an important r6le in tie- 

 development of the theory of the law of storms 

 which lies yet in the future. The height to which 

 storms extend in the atmosphere, as has been 

 shown from the lien Nevis observations, is greatly 

 less than had been supposed. 



Forecasting. Valuable aid in forecasting storms 

 and weather is derived from two important deduc- 

 tions from past observations : I. A cyclone tends 

 towards a path near to the anticyclone which lies 

 immediately to the right of the progressive motion 

 of the storm at the time. 1 1. When the rates of fall 

 of the barometer at stations in the west of Europe 

 are noted, it is found that the path taken by tin- 

 coming storm is indicated by those stations at which 

 the rates of fall of the barometer are greatest. 



Relation of Storms to the Character of the Sea- 

 son. This is vital and all-important. Thus, as 

 regards the British Islands, when the general path 

 pursued by storms in their easterly course over 

 Europe lies to the southward the winter is severe, 

 inasmuch as the British Islands are then on the 

 north side of the centre of low pressure, and con- 

 sequently in the stream of the northerly and 

 easterly winds which there prevail. On the other 

 hand, when the paths of storms lie to the north- 

 ward the British Islands are on the south side of 

 the low pressure, and therefore in the stream of 

 the warm, moist, southerly and south-westerly 

 winds which there prevail. The weather of 

 December 1890 and that of February 1891 illus- 

 trail 1 these two distinct types of weather. In 

 December 1890 the weather was colder in the 

 southern counties of England than it had been 

 during the present century. At Oxford the tem- 

 perature was 10-0 under the average, and in the 

 south-western provinces of Kussja the mean tem- 

 perature was fully 14 O" below the average. On 

 the other hand, to the north of a line drawn from 

 Wilna to Bergen temperature was above the 

 average, the excess above the mean increasing on 

 advancing northward till in the north of Norway 

 it was 10-0, and at the entrance of the White Sea 

 l:;-o . In the same month in the Eastern States 

 and Canada temijerature was under the average, 

 the deficiency lieing 11 -5 at Montreal; whereas 

 over the rest of (lie United States temperature 

 was high, the excess increasing on proceeding 

 northward till, in Assiniboia, it was from 14O" to 

 17O" above the average. The explanation is at 

 once afforded by the distribution of atmosphciic 

 pressure at the time. In Europe prcssiue was 

 unusually high from the north of Scotland to St 

 Petersburg. But, what is of more importance, it 

 diminished steadily southward over the continent 

 and into the north of Africa, and, on the other 

 hand, also diminished steadily over the north of 

 Europe, being 0-350 inch lower at the North Cape 

 than at Bergen. Consequently the whole of the 

 southern half of Europe was swept by northerly 

 and easterly winds, bitterly cold and dry, ami tem- 

 perature fell unprecedented!)' low ; but in the 

 north southerly and south-westerly winds inevit- 

 ably prevailed, bearing to the northern climes the 

 warmth of lower latitudes. In America atmo- 

 spheric pressure was alxive the average over a 

 broad area extending from New Orleans to Late 



