66 Tr ansae tions . — Miscellaneous . 



with it, hence the pressure is greater on the south than on 

 the north, and the whole system is forced northwards as well 

 as eastwards. As this upward whirl moves over the ocean 

 it is constantly sucking up watei'-vapour with the air which 

 enters it below. This is condensed in its turn as it rises into 

 regions of lower pressure and lower temperature, forming 

 clouds, rain, hail, or snow, and liberating more heat, and so 

 giving fresh force continually to the ascending current. The 

 ascending currents must be strongest on the north and east, 

 which are fed by warm air, and less strong on the south and 

 west, which are fed by cold air ; and this, probably, is the chief 

 cause of easterly and northerly motion. 



Our circular storms act as immense irrigating and warm- 

 ing machines, pouring out over sea and land the water taken 

 up as vapour, and diffusing the heat in the upper air originally 

 communicated by the sun to the upper layers of the ocean, 

 while at the same time they mix and purify the air. These 

 rotary storms are frequently met with by vessels navigating 

 the ocean south of the belt of anti-cyclones and high pressure. 

 Captain Maury collected an immense number of statistics on 

 the subject, which place it beyond doubt that they occur 

 frequently at least as far south as 50° or 55° S. latitude, 

 where, although west winds prevail, east winds sometimes 

 occur. 



In our latitudes they generally first become apparent to 

 our observation in the neighbourhood of Cape Leu win, whence 

 they advance eastwards along the border of the belt of anti- 

 cyclones, sometimes as rapidly as twelve hundred miles in the 

 twenty-four hours, or fifty miles an hour, sometimes much 

 more slowly. Sometimes they are stopped or even recede for 

 a time, apparently being resisted by the anti- cyclones. Some- 

 times they partially break through the barrier northwards, but 

 never completely, as far as I have been able to ascertain. 

 Most frequently the storms pass south of New Zealand ; but 

 very frequently they extend as far as Cook Strait, through 

 which they pass. More rarely they extend to the north of the 

 North Island, in which case they generally present the normal 

 type of a completely closed circulation, while those that pass 

 south of Wellington usually present the appearance of a 

 partial circulation open to the south. Probably this is fre- 

 quently due to our having no observatories farther south to 

 record the variations of barometric pressure and of the direc- 

 tion of the wind ; but sometimes the circuit may be open to 

 the south, as is the case occasionally in North America 

 towards the north. Always it is to be observed that our great 

 mountain-ranges largely influence the form and progress of 

 the storm circulation, and it would seem also that over the 

 ocean the progress and extension northwards of the depres- 



