Edwin. — Meteorology of New Zealand. 565 



movement of the belt shows that the wind-currents of the 

 Equatorial low pressure must mainly travel from the east- 

 ward. The mechanical movement is continued on the polar 

 side of both the high-pressure systems by belts of westerly 

 winds which extend round the earth ; but, owing to the 

 continual changes in the dimensions of the high pressures, 

 these belts of westerly winds are of varying width and 

 sinuous form, causing deflection of the westerly current to 

 between south-west and north-west in the Northern Hemi- 

 sphere, and to between north-west and south-west in the 

 Southern Hemisphere, resulting in wavelike depressions whose 

 route is towards east. Pressure within both of these belts 

 decreases polewards, and their latitudinal limits extend from 

 the edges of the anticyclonic belts to between the 60th and 

 70th degrees of both north and south latitudes. 



Cyclones originate within the limits of the Equatorial belt, 

 and in both hemispheres travel first towards the west, those 

 of the Northern Hemisphere curving gradually toward north 

 and east, those of the Southern Hemisphere toward south and 

 east. Some of these disturbances have sufficient energy to 

 force their way between the systems of the anticyclone belts 

 and into the regions of the westerly winds, to which they 

 convey both heat and moisture. 



Continuing the consideration of mechanical effort, it is evi- 

 dent that the rotation of the two discs is such that the move- 

 ment of their poleward edges is towards the right — i.e., to the 

 eastward — therefore a belt resting on these edges must move 

 parallel to them, and to this movement the west- wind belts 

 correspond. 



On the northern side of the west- wind belt of the Northern 

 Hemisphere, and on the southern side of that of the Southern 

 Hemisphere, pressure is lower than in all other regions, and 

 therefore it should seem that there should be continuous wes- 

 terly winds circulating round a minimum pressure at each 

 pole. But it is well known that easterly winds are experienced 

 in very high latitudes, and from this it is evident that some 

 other arrangement of winds and pressure exists within these 

 areas. Further consideration of the mechanical effort already 

 mentioned will show that the movement of the west-wind belts 

 must influence whatever pressures he poleward of them, and 

 that their action on a disc lying between them and the pole 

 would be to cause the disc to rotate from right to left — i.e., 

 from west to east — and therefore the edge nearest the pole 

 must move from east to west. This rotation corresponds to 

 the wind-revolution of the anticyclone of the opposite hemi- 

 sphere, and must be accompanied by an increase of pressure 

 toward the centre of the disc, although pressure within that 

 area is low. 



