The Winds. 257 



eight more complete revolutions in one direction than it has 

 in the other. 



Enough has been said in this article to explain, in a general 

 manner, the nature and office of the winds. A few words on 

 premonitory signs will show by what appearances, and to what 

 extent (apart from instruments), their arrival may often be 

 predicted. 



South-west gales reach the British Isles from warm and 

 moist regions of the Atlantic, in the direction of the Azores. 

 They shelve upwards by their levity as they approach, and the 

 phases of the advancing current can be traced by the growing 

 streaks of cirrus in the upper air. The wind, at first in the 

 north-east, veers very slowly through the east towards the 

 south, and the blue curtain of the sky appears lined with bands 

 of cirro-stratus cloud, stretching from horizon to horizon across 

 the direction of the upper wind. Halos of every form, and a 

 narrow border of light surrounding the moon, are a symptom 

 of this condition of the wind. If these signs are remarkable 

 for brightness or extent, and the clouds thicken, they take 

 the form of cirro-cumulus, or a cc mackerel-backed" sky, and 

 are followed by severe falls of rain, hail, or snow, on the 

 arrival of the wind. 



North-east gales arrive upon the British coasts from colder 

 climates, and from their greater gravity creep along the ground. 

 Driving off the warmer air, they at first create dense clouds, 

 or, contending with a southerly current, lightning, rain, and 

 snow are produced, and the wind, at first south-west, veers 

 rapidly through west towards the north. When the northerly 

 current is established, fine weather reappears. Coronas, or 

 highly-coloured circles round the moon in ragged clouds that 

 scud before a north-west wind, indicate a liability of this wind 

 to " back," and for the same order to begin again. 



Lightning is always caused by the sudden condensation of 

 vapour into rain ; and the more rapid this process, the more 

 severe is the lightning. Hail occurs in sultry weather, when 

 aqueous vapour reaches a great height, and becomes entangled 

 in currents of low temperature. That these storms in the 

 upper air are often of a violent character may be inferred from 

 what is related by Olmsted in America, Buist at Bombay, aud 

 JSTeumayer at Melbourne, in South Australia, that hailstones as 

 large as pigeon's eggs are of annual occurrence. 



With hail, as with rain, the tension of electricity on the 

 surface increases in the exact ratio of the diameter of the drop. 

 The present year was distinguished by two instances of hailstones 

 of extraordinary dimensions, accompanied by very destructive 

 lightning, at Liverpool and at Birmingham, on the 21st of May 

 and 8th of July. One of the greatest falls of hail, since the 



VOL. VIII. — NO. IV. S 



