678 REMAEKS ON THE BAROMETER. 



from the north-westward, northward, or north-eastward, after which 

 violence a rising glass foretells improving weather, if the Thermometer falls. 

 But, if the warmth continue, probably the wind will back (shift against 

 the sun's course), and more southerly, or south-westerly wind will follow.* 



The most dangerous shifts of wind, and the heaviest northerly f gales, 

 happen after the mercury first rises from a very low point. 



Indications of approaching changes of weather, and the direction and 

 force of winds, are shown less by the height of mercury in the tube, than 

 by its falling or rising. Nevertheless, a height of about thirty inches (at 

 the level of the sea) is indicative of fine weather and moderate winds. 



The Barometer is said to be falling when the mercury in the tube is 

 sinking, at which time its upper surface is sometimes concave or hollow. 

 The Barometer is rising when the mercurial column is lengthening ; its 

 upper surface being then, as usual, convex or rounded. J 



A rapid rise of the Barometer indicates unsettled weather. A slow rise, 

 or steadiness, with dryness, shows fair weather. 



A considerable and rapid fall is a sign of stormy weather and rain. 

 Alternate rising and sinking show very unsettled weather. 



The greatest depressions of the Barometer are with gales from the S.E., 

 southward, or S.W. ; the greatest elevations, with winds from the N.W., 

 northward, or N.E. 



Although the Barometer generally falls with a southerly and rises with 

 a northerly wind, the contrary sometimes occurs ; in which cases the 

 southerly wind is dry and the weather fine ; or the northerly wind is wet 

 and violent. 



When the Barometer sinks considerably, high wind, rain, or snow will 

 follow ; the wind will be from the northward, if the Thermometer is low 

 (for the season) — from the southward if the Thermometer is high. 



Sudden falls of the Barometer, with a westerly wind, are sometimes 

 followed by violent storms from N.W. or North. 



If a gale sets in from the eastward or S.E., and the wind veers by the 

 South, the Barometer will continue falling until the wind becomes S.W., 

 when a comparative lull may occur, after which the gale will be renewed ; 

 and the shifting of the wind towards the N.W, will be indicated by a fall 

 of the Thermometer as well as a rise of the Barometer. 



Three things appear to affect the mercury in a Barometer : — 



1. The direction of the wind — the N.E. wind tending to raise it most — 

 the S.W. to lower it the most, and winds from points of the compass between 

 them proportionally as they are nearer one or the other extreme point ; 

 N.E. and S.W. may therefore be called the wind's extreme bearing. 



The range, or difference of height of the mercury, due to change of 

 direction only, from one of these bearings to the other (supposing strength 

 or force, and moisture, to remain the same), amounts in these latitudes to 

 about half an inch (shown by the Barometer as read off). 



• In an Aneroid, a metallic, or a ■wheel Barometer, the motion of the hand should 

 correspond to that of the mercury in an independent instrument. 



t Southerly in South latitude. 



I In the best columns, those of standards for example, no concavity is seen at any 

 time. 



