V.— PHYSICS. 



Art. LIX. — Meteorology of New Zealand : On the Boutes of 

 High and Low Pressures, and the Changes of Pressure 

 and Wind-movement resulting from them. 



By Eetired Commander E. A. Edwin, E.N., Weather Eeporter. 

 [Read before the Wellington Philosophical Society, 3rd August, 1904.] 



In describing the changes of both pressure and wind which 

 occur in this colony it is first of all necessary to describe 

 the principles upon which the atmospheric movements which 

 bring about these changes are carried out. 



There are two divisions of atmospheric pressure — viz., high 

 and low. The former are termed " anticyclones," and consist 

 of separate systems which are generally of an irregularly 

 shaped circular, and sometimes of elliptical, form, and within 

 which pressure is always above 30 in., increasing concentrically 

 inward to a maximum point. Their progression is always 

 from west to east, and in this hemisphere their wind-rotation 

 is from right to left, or as against the hands of a watch. 



Low pressures are all systems having pressure below 

 30 in., and are of two kinds : (1.) Cyclonic, in which pressure 

 is considered to be arranged spirally, and decreasing to a cen- 

 tral minimum area. In these low pressures the wind is also 

 considered as being arranged spirally, and in this hemisphere 

 both move from left to right, or similarly to the movement of 

 watch-hands. They originate within the Tropic of Capricorn, 

 between the Equator and about 8° of south latitude, and their 

 route is first toward a little southward of west, curving to- 

 wards south-west and south, and finally to south-east. 

 (2.) Westerly low pressures, in the form of waves, in which 

 pressure is oscillatory, and is in this hemisphere always 

 lowest towards the Pole. Their winds are also oscillatory, 

 ranging from the north through west towards south, and back 

 through the west towards north. Neither wind nor pressure 

 has any definite period of duration, but their changes are 

 regular, pressure always diminishing when the wind moves 

 from the north towards west, and increasing with winds 

 between west and south. The movement back to north is 

 often accomplished so quickly that pressure seems to be in- 

 creasing also during that time. 



The wind and pressure movements of an anticyclone of 

 this hemisphere are illustrated by fig. 1, which shows these 

 changes as the high pressure moves from west towards east 

 over three positions, a, b, and c, considered as being situated 



