1862.] on Meteorological Telegraphy, 449 



tlierefore, great differences of pressure (or tension) shown by barometer 

 of temperature, of dryness, or moisture, and direction of wind, should 

 be considered as signs of changes^ likely to occur soon. 



It will be observed, on any continued comparison of weather 

 reports, that during- the stronger winds a far greater degree of 

 uniformity and regularity is shown than during the prevalence of 

 moderate or light breezes : and this should be remembered. 



When neither of the greater and more extensive atmospheric 

 currents is sweeping across the British Islands, — currents of which the 

 causes are remote, and on a large scale, — the nature or ciiaracter of 

 our winds approaches, and is rather like that of land and sea breezes 

 in low latitudes ; especially in summer. 



Either the cooler sea wind is drawn in, over land heated by the 

 summer sun ; or cold air from frosty heights, snow-covered lands, or 

 chilly valleys, moves towards the sea, which is so uniform in tempera- 

 ture for many weeks together, changing so slowly , and but little, in 

 comparison with land, during^ the year. These light variables may at 

 such times be numerous, simultaneously, around the compass, on the 

 various coasts of the British Islands. 



Frequently it has been asked, " In this country, how much rise or 

 fall of the glasses may foretell remarkable change, or a dangerous 

 storm ? " 



To which can now be replied, — great changes or storms are usually 

 shown by falls of barometer exceeding an inch ; and by differences of 

 temperature exceeding about fifteen degrees. A tenth of an inch an 

 hour is a fall indicating a storm or very heavy rain. The more 

 rapidly such changes occur, the more risk there is of dangerous atmo- 

 spheric commotion. 



As all barometric instruments often, if not usually, show what may 

 be expected a day or even days in advance, rather than the weather of 

 the present or next few hours, and as winil, or its direction, affects 

 them much more than rain or snow, due allowance should always be 

 made for days as well as for hours to come. 



The general effect of storms is felt unequally in our islands, and less 

 inland than on the coasts. Lord Wrottesley has shown, by the ane- 

 mometer at his observatory in Staffordshire, that wind is diminished or 

 checked by its passage over land. The mountain ranges of Wales and 

 Scotland, rising two to four thousand feet above the ocean level, must 

 have great power to alter the direction, and probably the velocity of 

 wind, independently of alterations caused by changes of temperature. 



" It not unfrequently happens that a series of cyclones follow closely 

 upon each other for several weeks, the preceding members of the 

 series being often overtaken and interfered with by those succeeding. 

 It is, however, important to remark, that amidst all the complexity 

 necessarily occasioned by such combinations — the greater and more 

 violent storms, and particularly that portion of them which is most 

 dangerous and destructive, exhibit almost invariably the simple cyclonic 

 character. It is thus with the ' Law of Storms ' as with the ' Law of 



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