130 Philosophy of Storms. 



will cause the air to run in below towards the equator, and of 

 course rise there. Now from the principle of the conservation of 

 areas, it will fall more and more to the west as it rises, and of 

 course the upper current of the air, at the equator probably moves 

 towards the west. 



However, as the air rolls off above, towards the north, it will 

 be constantly passing over portions of the earth's surface, which 

 have a less diurnal velocity than the part from which it set out, 

 and as from the nature of inertia it still inclines to retain the di- 

 urnal velocity towards the east which it originally possessed, 

 when it reaches the latitude of about 20° or 25°, it will then pro- 

 bably be moving nearly towards the north — and beyond that lat- 

 itude its motion will be to the northeasterly. 



If violent storm clouds, which necessarily rise to a great height 

 into the upper current, are driven forward in the direction of the 

 upper current, it is probable that the barometer will rise higher in 

 that part of the annulus which is in front of the storm, than in 

 the rear, and if so, a sudden rise of the barometer in particular 

 localities, may become, when properly understood, one of the first 

 symptoms of an approaching storm. 



In consequence of the high barometer in front of the storm in 

 a semi-annulus, the air will be forced downwards there, and 

 cause in some cases a more violent action of the air or wind 

 backwards, meeting the approaching storm, than will be experi- 

 enced, in the rear of the storm. 



As the air comes downwards in the semi-annulus in front of 

 the storm, it will come under greater pressure, and therefore any 

 clouds which it may contain, will probably be dissolved, by the 

 heat of greater pressure, and therefore on the passage of the annu- 

 lus, it will probably be fair weather. 



Also, as the air above always contains more caloric to the 

 pound, than the air below, there will be an increase of tempera- 

 ture on the passage of the annulus, partly from the increased 

 pressure, but chiefly by the descent of the air ; in very hot cli- 

 mates this increase of temperature, in front of the storm, will be 

 very sensibly felt. 



The increased pressure in the annulus round a volcano, when 

 it suddenly bursts out, will sometimes under favorable circum- 

 stances, be very great, and of course the air will be depressed 

 from a great height, so that some portion of the very air which 

 has gone up in the central parts of the ascending column, and 



