154 CYCLONES. 
due north wind into a north-easterly one. A good illustration of . 
this is found in the well-known north-east trade winds. These _ 
winds, which blow from about latitude 30° north towards the 
equator (to fill the vacuum caused by the rising of the heated air 
over that portion of the earth), would be due north winds if it 
were not for the rotation of the earth, which converts them into 
north-easterly winds. It is, then, evident that all winds blowing 
from the south are always inclining to a south-westerly direction, 
and all winds from the north are inclining to a north-easterly 
direction. (East and west winds will not be affected by the 
earth’s rotation, as they keep to a portion of the earth that is 
moving at a constant speed.) Now let us consider a Cyclone just 
formed, in which, as I have shown, air is rushing towards the 
centre from all directions. It will be easily seen, then, that all the 
wind coming in towards the Cyclone from the south must have a 
general inclination to press /owards the east of the Cyclone (from 
the reasons I have just given), and all the wind coming from the 
north must have an inclination to press towards the west. Now 
imagine, for a moment, that the Cyclone (Fig. 1) is a cart 
wheel that easily turns on its axis. On the south side of it 
press it ‘owards the east, as the south winds will do, and on the 
north of it press it sowards the west, as the north winds will do, 
you will then see that the whole system would commence to turn 
round in an offostte direction to the hands of a watch. The 
rotation of the earth is, then, the cause of the direction of rotation 
of the wind round a Cyclone. 
So far I have only spoken of Cyclonic wind movements in the 
northern hemisphere of our world. But if we go south of the 
equator, we must expect different movements of the wind in 
Cyclones. For here the movement of wind, from the equator 
towards the south pole, will, owing to the rotation of the earth, be 
changed from north to a north-westerly wind ; and from the same 
cause the wind blowing from the south will become south-easterly. 
Ifyou will consider for a moment what the effect of these directions 
of the wind will be on a Cyclone just formed, you will find that 
the rotation of the wind round the Cyclone would be in the same 
