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 somethi 
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 avi 
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, 
