ADDENDUM, 



Teansactions op Section A — continued. 



Note. — The following absti-act arrived too late for insertion in its proper 

 place in the report. It is intended to replace the short abstract 

 printed at page 78. 



On the GJiaracteristics of the Nor'-icestcrs of Canterbury, 

 New Zealand. 



By J. T. Meeson, B.A. 



The general features of a typical nor'-wester, as experienced in 

 Christchurch, have, unfortunately, this season been only too 

 familiar to us all. It is, therefore, not necessary to repeat 

 here the full description of the phenomena with which the 

 author commenced his paper. The thermometrical, barome- 

 trical, nephological, and other effects of the nor'-wester having 

 been given, the high temperature of the wind was next ex- 

 plained. It had been customary to account for it as the 

 result of compression on the eastern side of the Southern 

 Alps, for it was well known that dry air in descending gained 

 heat at the rate of 1° Fahr. for every 180ft. of vertical measure- 

 ment. The pneumatic tinder-box clearly enough showed that 

 compression resulted in heat. But compression on one side 

 of the mountains only restored the temperature lost by 

 expansion on the other side — provided the air on both sides 

 were subject to the same conditions of barometric pressure, 

 temperature, velocity, and humidity. Here, however, came in 

 a point of the greatest importance. The north-west wind, on 

 reaching the western slopes of the Southern Alps, was heavily 

 charged with moisture, and this rendered latent the heat 

 brought by the wind from the lower latitudes. Now, wet air 

 in an ascending current lost heat much more slowly than dry 

 — namely, 1° Fahr. for every 300ft. of altitude ; because the 

 expansion during ascent resulted in the precipitation of rain, 

 and thus latent heat was rendered sensible. This difference in 

 the rate of losing and gaining heat on the part of wet and dry 

 air was the chief immediate cause of the uncomfortable warmth 

 of our nor'-westers ; for, assuming that the wind in Westland 

 38 



