XV111 INTRODUCTION. 



appearances 6 and 7, and its parts will be seen spreading outwards 

 in all directions, especially on that side towards which the upper 

 current is moving, assuming something of the shape of a mush- 

 room. In the mean time, the action of the in-moving current be- 

 low, and upmoving current in the middle, will become very vio- 

 lent, and if the barometer falls two inches under the, centre of the 

 cloud, the air, on coming in under the cloud, will cool by dimin- 

 ished pressure about ten degrees, and the base of the cloud will 

 reach the earth, if the dew point was only eight degrees 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 invert- 

 ed cone with its apex on the ground, as 8, and when a little more 

 prolonged and fully developed, it will be what is called a torna- 

 do if it is on land, and a water-spout if at sea. 



On visiting the path of a tornado, (see the whole of section 

 VII.) 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, 

 or parallel to the path ; and invariably if one tree lies across an- 

 other, the one which is thrown backwards is underneath. Those 

 materials on the sides which are moved from their places and roll- 

 ed 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, being carried beyond the centre by their momentum, and 

 moved a little forward by the rear 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. 

 On examining the trees which stand near the borders of the path, 

 it will be found that many of the limbs are twisted round the trees, 

 and broken in such a manner as to remain twisted, those on the 

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

 of the path from right to left. However, it will be found that only 

 those limbs which grew on the side of the tree most distant from 

 the path of the tornado are broken; for those alone were subject 

 to a transverse strain. The houses which stood near the middle 

 of the path will be very liable to have the roofs blown up, and 

 many of the walls will be prostrated, all outwards, by the explo- 

 sive influence of the air within, and those houses covered with 



