TRANSACTIONS OF SECTION A. 7$ 



mountains would be similar in both cases. It therefore, as 

 far as our present investigation is concerned, does not seem 

 very important whether we adopt the rotary theory of Redfield 

 or the inhloxving theory of Espy. Dove certainly seems to 

 speak of gales as something quite distinct from the cyclones of 

 Piddington. But, as has been remarked, " the law of storms 

 is the law of wind everywhere," and the terms " gale," 

 " cyclone," and " tromb " only indicate similar movements of 

 the atmosphere affecting areas of different magnitudes. A 

 gale, in fact, may be assumed to be a portion of a huge cyclone 

 whose true character is concealed from us because we are not 

 able to carry on sufficiently wide simultaneous observations. 

 The true cyclone itself is perhaps popularly misunderstood. It 

 does not necessarily imply the violence of the tempest or 

 hurricane, such violence only occurring when the isobars are 

 very near — that is, when the depression is deep and the baric 

 gradient steep. It sometimes is as much as 0'2, though the 

 normal rate of barometric change is not more than 0'02 to 

 more than 0-05. 



Do our violent north-westers evidence the passing of 

 cyclones over our heads to the south-east ? Loomis and other 

 meteorologists agree that storms as a rule in our latitude 

 travel to the eastward — to the north-east in the Northern 

 Hemisphere, to the south-east in the Southern. They make 

 their way in that direction because of the rotation of the earth, 

 the rain being drawn eastward, Blasius thinks, by traction of 

 deficient air. That being so, however, I do not think that 

 many of our north-west cyclones pass directly over Canterbury 

 to the south-east, for the following reasons : It is very seldom 

 indeed that the wind goes suddenly round from north-west to 

 south-east, or that the central calm of the cyclone is observable, 

 which would always be the case if we were here in the direct 

 path of the storm. Eain falls also very rarely, and the fall of 

 the rain determines, or is supposed to determine, to a large 

 extent the path of the disturbance ; for it gives out heat and 

 thus causes the air to expand and whirl upwards, making a 

 comparative vacuum which the air behind fills, and so the 

 direction of the whole slanting and inverted aerial whirlpool 

 is determined. 



What Loomis says about rain or snow on the west side 

 retarding the progress of a cyclone is instructive. It favours 

 the idea that our north-west storms, through the heavy rain 

 they deposit on the Southern Alps, are stopped, worn out by 

 dashing against or amongst the mountains, or else diverted, as 

 already observed, along the coast-line and the flanks of the 

 range. North-westers are experienced in the Chatham 

 Islands, but there, as on the west coast of New Zealand, 

 they are the rain-bringers and quite different from our dry 



