ScHAw. — A Wellington Weather Prognostic. 73 



and the whole system, extending, it may be, over one thou- 

 sand or even two thousand miles of the earth's surface every 

 way, is moving rapidly to the eastward. The rate of east- 

 ward progress averages about five hundred miles in the twenty- 

 four hours. This causes the variations in the direction of 

 the wind and in the height of the barometer. But the force 

 of the wind varies with the rotary motion. The wind at the 

 front of a cyclone approaching us from the west must be from 

 the northward or north-westward if, as is almost always the 

 case, the centre of the storm is not to the north of us. Very 

 generally it is south of New Zealand altogether. Very rarely 

 it is north of Wellmgton, and in these rare cases, when the 

 storm would begin with a north-east wind, changing by 

 east to south, probably the characteristic fish clouds would 

 not appear. 



For I imagine that their history is somewhat like this : As 

 the cyclone advances from the west, warm, moist air is drawn 

 in below from the north on that side of the eddy ; it is whirled 

 onward, upward, and southward until it reaches a cold level, 

 where its water- vapour is condensed into clouds, and the dry 

 air pouring over them smooths down their upper surfaces into 

 the fish-back forms which we observe. 



This seems to me a probable explanation of the way in 

 which these clouds are formed on the north-eastern edge of an 

 advancing cyclone here, and of the reason why their appear- 

 ance should be a usual precursor of a north-westerly blow 

 with a falling barometer, to be succeeded by a southerly blow 

 with a rising barometer, as usually happens. The cause I 

 have assigned is, of course, conjectural, but it seems to me 

 reasonable ; and, if it be true, the same weather prognostic 

 ought, I think, to be true all up the west coast of this Island, 

 and probably as far as ^Westport on the west coast of the 

 South Island, or even farther south. On the east coast, or 

 inland, probably this form of cloud would not be so usual or 

 characteristic, as the advancing cyclone circulation is, as we 

 know, much broken up by the great mountain barrier running 

 nearlv north and south throuerh these Islands, and the indraught 

 of air would be modified by the land-surface over which it must 

 pass. The break in this barrier at Cook Strait and the direc- 

 tion of our coast-line here are undoubtedly the causes of the 

 prevailing northerly or southerly winds experienced here, the 

 westerly winds being deflected north or south, and easterly 

 winds very rarely occurring, because, as before observed, the 

 centres of the cyclones usually are to the south of us. 



