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8.— REMARKS ON THE BAROMETER 



By the late Admiral FitzBoy, F.B.S* 



The words on the scales of Barometers should not be so much regarded 

 for weather indications, as the rising^ or falling of the mercury. For if it 

 stand at Changeable, and then rise towards Fair, it presages a change of 

 wind or weather, though not so great as if the mercury had risen higher ; 

 and, on the contrary, if the mercury stand above Fair and then fall, it 

 presages a change, though not to so great a degree as if it had stood lower; 

 besides which, the direction and force of wind are not in any way noticed. 

 It is not from the point at which the mercury may stand that we are alone 

 to form a judgment of the state of the weather, but from its rising or 

 falling ; and from the movements of immediately preceding days, as well 

 as hours, keeping in mind effects of change of direction, and dryness, or 

 moisture, as well as alteration of force or strength of wind. 



In Western Europe, towards the higher latitudes, the quicksilver ranges, 

 or rises and falls, nearly three inches — namely, between about thirty inches 

 and eight-tenths (30-8), and less than twenty-eight inches (28-0) on extra- 

 ordinary occasions ; but the usual range is from about thirty inches and a 

 half (30-5) to about twenty-nine inches. Near the Line, or in Equatorial 

 regions, the range is but a few tenths, except in storms, when it some- 

 times falls to twenty-seven inches. 



The sliding-scale (vernier) divides the tenths into ten parts each, or 

 hundredths of an inch. The number of divisions on the vernier exceeds 

 that in an equal space of the fixed scale by one. 



If the Barometer has been about its ordinary height, say near thirty 

 inches, at the sea-level,f and is steady, or rising — while the Thermometer 

 falls, and dampness becomes less — north-westerly, northerly, or north- 

 easterly wind — or less wind — may be expected. 



On the contrary, if a fall takes place, with a rising Thermometer and 

 increased dampness, wind and rain (or snow) may be expected from thff 

 south-eastward, southward, or south-westward. 



Exceptions to these rules occur when a north-easterly wind, with wet 

 (rain or snow), is impending, before which the Barometer often rises (on 

 account of the direction of the coming wind alone), and deceives persons 

 who, from that sign only, expect fair weather. 



When the Barometer is rather below its ordinary height, say, near 

 twenty-nine inches and a half (at the sea-level only), a rise foretells less 

 wind, or a change in its direction toward the northward — or less wet ; but 

 when the mercury has been low, say near twenty-nine inches, the first 

 rising usually precedes and foretells strong wind — (at times heavy squalls) 



* It must be remembered that these remarks were written previous to the discovery 

 of the Cyclonic and Anti-cyclonic systems of Storms (page 198), which cross our islands. 

 They are, however, quite in agreement with these systems. 



t It stands lower, about one-tenth of an inch for each 100 feet of height directly 

 upwards, or vertically, above the sea, where its average height, in England, is 29-94 

 inches (at 32° F.). 



