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On Tropical and Extra-Tropical Cyclones. [Feb. 24 r 



The general character of the cloud all round the centre is more 

 uniform in than out of the tropics ; but still the clouds in rear are 

 always a little harder than those in front. 



Everywhere the rain of a cyclone extends farther in front than in 

 rear. Cyclone rain has a specific character, quite different from that 

 of showers or thunderstorms ; and this character is more pronounced 

 in tropical than in extra-tropical cyclones. 



Thunder or lightning is rarely observed in the heart of any 

 cyclone, and the absence of electrical discharge is a very bad sign of 

 the weather. Thunderstorms are, however, abundantly developed on 

 the outskirts of tropical hurricanes. 



Squalls are one of the most characteristic features of a tropical 

 cyclone, where they surround the centre on all sides ; whereas in 

 Great Britain, squalls are almost exclusively formed along that portion 

 of the line of the trough which is south of the centre, and in the 

 right rear of the depression. As, however, we find that the front of 

 a British cyclone tends to form squalls when the intensity is very 

 great, the inference seems justifiable that this feature of tropical 

 hurricanes is simply due to their exceptional intensity. 



A patch of blue sky, commonly known as the " bull's-eye," is 

 almost universal in the tropics, and apparently unknown in higher 

 latitudes. The author's researches show that in middle latitudes the 

 formation of a u bull's- eye" does not take place when the motion of 

 translation is rapid ; but as this blue space is not observed in British 

 cyclones when they are moving slowly, it would appear that a certain 

 intensity of rotation is necessary to develope this phenomenon. 



The trough phenomena, — such as a squall, a sudden shift of wind, 

 and change of cloud character and temperature, just as the barometer 

 turns to rise, even far from the centre — which are such a prominent 

 feature in British cyclones, have not been even noticed by many meteor- 

 ologists in the tropics. The author, however, shows that there are 

 slight indications of these phenomena everywhere ; and he has collated 

 their existence and intensity with the velocity of propagation of the 

 whole mass of the cyclone. 



Every cyclone has a double symmetry. One set of phenomena, 

 such as the oval shape, the general rotation of the wind, the cloud 

 ring, rain area, and central blue space, are more or less related to a 

 central point. 



Another set, such as temperature, humidity, the general character 

 of the clouds, certain shifts of wind, and a particular line of squalls, 

 are more or less related to the front and rear of the line of the trough 

 of a cyclone. 



The author's researches show that the first set are strongly marked 

 in the tropics, where the circulating energy of the air is great, and 

 the velocity of propagation small ; while the second set are most 



