594 REPORT— 1891. 



was at 60° Falir., on reaching 9,000ft. in elevation it would fall 

 to 30° — i.e., ''7fo°o°° would be lost— and on reaching Christ- 

 church there would be an increment of ^y£^° Fahr. — i.e., 50° 

 Fahr. — which would make, with the 30° Fahr. retained at 

 the summit of the Alps, a temperature of 80°. This reasoning 

 was first given by Espy and Maury (in 1861) without special 

 application, and Dr. Hann, Herschell, and others subse- 

 quently used it to explain the fohn wind of Switzerland, a 

 quite analogous wind, which even Dove had failed to account 

 for satisfactorily. This reasoning applied to our nor'-wester, 

 which was a true fohn. But even that explanation did 

 not get to the root of the matter, for it only showed how 

 heavy rain in Westland rendered sensible in Canterbury 

 the heat previously latent. Therefore the question still re- 

 mained. Whence came that heat ? It was brought from the 

 tropics. The hot equatorial wind or return trade, also, in cross- 

 ing warm oceanic currents, gathered up further moisture and 

 heat as it travelled to higher latitudes. Furthermore, the north- 

 west weather wtis mostly cyclonic, and all meteorologists 

 agree that, whatever the cause might be — aiad as yet it was 

 unexplained — a peculiar kind of stifling oppressive heat, giving 

 neuralgia, headache, rheumatism, &c., invariably was developed 

 on the front of a cyclone. In the Southern Hemisphere this 

 heat-spot would be found on the left front of the path of the 

 storm, and, granting that the cyclones producing our nor'- 

 westers sheered off to the south of New Zealand, beiag divertd 

 by the Southern Alps, we should be justified in locating the 

 heat-patch over the Canterbury Plains. Cold nor'-westers 

 occurred occasionally, and were sometimes probably only .local. 

 If they occurred in winter, when the initial heat of the winds 

 was great, and little precipitation on the mountains accompanied 

 them, they w^ere not difficult to understand ; but they occurred 

 at other seasons, and were then not easy to explain. The 

 clouds of dust which made a nor'-wester so unpleasant were 

 thought by Sir J. von Haast— probably erroneously — to explain 

 the loess formation of the Lyttelton hills and elsewhere. The 

 remarkable fall of the barometer on the approach and during 

 the continuance of a nor'-wester accorded with Dove's law of 

 the Southern Hemisphere generally — the steepness of the 

 baric gradient indicating the intensity of the disturbance. The 

 glass usually went down to 29-2in., and once quite recently had 

 even descended to 28-68in., though in twenty-four hours, when 

 south-west intervened, it had risen to 30in. again. Why the 

 glass fell in a nor'-wester was a difficult question. Maury's ex- 

 planation about aqueous vapour driving out and being lighter 

 than air did not meet the case so well as what Loomis said 

 about light hot air filling the whole space usually occupied 

 by colder and denser air. The north-west arch of clouds, a very 



