Philosophy of Storms. ^ 127 



an up-moving current is once formed, it will go on and increase in 

 violence, as it acquires perpendicular elevation, especially after 

 the cloud begins to form. At first the base of the cloud will be 

 flat ; but after the cloud becomes of great perpendicular diameter, 

 and the barometer begins to fall considerably, as it will do from 

 the specific levity of the air in the cloud, then the air will not 

 have to rise so far as it did at the moment when the cloud began 

 to form, before it reaches high enough to form cloud from the 

 cold of diminished pressure. 



The cloud will now be convex below, and its upper parts will 

 be seen spreading outward in all directions, especially on that side 

 towards which the upper current is moving, assuming something 

 of the shape of a mushroom. In the mean time the action of 

 the inmoving current below and upmoving current in the middle 

 will become very violent, and if the barometer falls two inches 

 under the centre of the cloud, the air will cool about 10°, and the 

 base of the cloud will reach the earth if the dew point was only 

 8° below the temperature of the air at the time the cloud began 

 to form. The shape of the lower part of the cloud will now be 

 that of an inverted cone with its apex on the ground, and it will 

 be what is called a tornado if it is on land, and a water-spout if 

 at sea. 



On visiting the path of a tornado, the trees on the extreme 

 borders will all be found prostrated with their tops inwards, either 

 inwards and backwards, or inwards and forwards, or exactly 

 transverse to the path. The trees in the centre of the path will 

 be thrown either backwards or forwards parallel to the path ; and 

 invariably if one tree lies across another, the one which is thrown 

 backwards is underneath. Those materials on the sides which 

 are moved from their places and rolled along the ground, leaving 

 a trace of their motion, will move in a curve convex behind ; those 

 which were on the right hand of the path, will make a curve 

 from left hand to right, and those on the left hand of the path 

 will make a curve from right hand to left, and many of these 

 materials will be found on the opposite side of the path from that 

 on which they stood on the approach of the tornado. Also, those 

 bodies which are carried up will appear to whirl, unless they arise 

 from the very centre — those that are taken up on the right of the 

 centre will whirl in a spiral from left to right, and those on the 

 left of the centre, will whirl in a spiral upwards from right to left. 



