186 OBSEEVATIONS ON THE WINDS. 



which and the storm which has passed away the wind has veered from 

 S.W. to West and N.W., accompanied by a fast-rising barometer and 

 generally very fine weather. The first indication of there being another 

 storm to the Westward of the ridge is given by the appearance of cirrus 

 clouds, which generally move from the N.W. or West. When the crest of 

 the ridge has passed, the barometer begins to fall, and the wind backs to 

 the Southward of West as the Eastern side of the incoming storm-centre 

 approaches the observer." 



(122.) The following remarks are taken from the section on Cyclonic 

 Gales of the North Temperate Zone, given in the " Barometer Manual." 



These gales generally commence at South, and end at West or N.W., 

 with little or no East wind. The probable reason of this is that the areas 

 of low pressure to which they are related have steep gradients only on their 

 East, S.E., South, and S.W. sides, there being little or no difi"erence of 

 pressure between their centre and the more permanent depression which 

 lies to the North of them. 



Whenever areas of both high and low pressure are liable to pass over any 

 region it is obvious that the direction of the wind, taken alone, will not be 

 a sufficient guide as to what weather is to be expected. If, for instance, 

 in the Northern Hemisphere, an area of high pressure be passing off to the 

 Eastward, the wind in the rear of it will veer through S.E. to South. 

 Although this direction of the wind shows that the barometrical readings 

 are lower to the Westward than to the Eastward, it is not by any means 

 an indication that a serious diminution of pressure, which may possibly 

 bring a Storm with it, is approaching, although the wind in front of such a 

 depression would be Southerly also. It is therefore necessary in such 

 circumstances to look for other signs, besides the mere direction of the 

 wind, when striving to foresee what is coming. 



Moreover, it must always be remembered that, although it is most com- 

 monly in connexion with considerable falls of the barometer that severe 

 Storms are experienced, yet the sudden large increase of pressure which 

 not infrequently follows such depressions, or takes place in their proximity, 

 may be accompanied by very violent winds. Caution, therefore, will always 

 be requisite on the occasion of any sudden change of pressure, whether it 

 be in the direction of increase or decrease. 



The Cyclonic Storms of the Temperate Zones do not often present the 

 phenomena of a central calm, with the winds blowing from nearly opposite 

 directions on each side of it. There is, therefore, not so much risk of being 

 taken aback as in the Tropical Cyclones ; the tack on which it will be safest 

 to lie-to, if obliged to do so, will be the same as that for the Cyclones (to 

 the Chapter on which the reader is referred). 



The most serious sudden shift of wind which is to be expected in these 

 Storms is that from S.W. to N.W., in the Northern Hemisphere. This is 

 generally accompanied by heavy rain or hail, with thunder and lightning, 

 while the temperature falls several degrees with the first blast of the N.W. 

 wind. 



In considering how to act in such circumstances, there are two matters 

 to which the seaman's attention should be directed, as they seriously affect 

 the conclusions he should draw from his barometer readings. 



