Tropical and Extra-tropical Cyclones. 



9 



As the cyclone approaches, a peculiar uneasy way of blowing of the 

 wind is sometimes reported, and the sky grows dirtier and dirtier till 

 the rain appears to grow out of the air. This has always been de- 

 scribed to the author as characteristic of cyclone rain, in opposition to 

 the showery rain from cumuloform clouds which is typical of the 

 ordinary precipitation of the monsoon. 



This peculiar cyclone rain seems to be only an intensification of the 

 rain associated with cyclones in Great Britain. There we see the 

 blue sky grow pale and sickly, and then grey, till rain falls from a 

 uniform gloom, and not from any defined cloud. In thunderstorm 

 rain, on the contrary, we see mountainous cumulus above the rain. 



Sometimes the front of an Indian cyclone is accompanied by thunder 

 and lightning ; but all observers are agreed that the absence of elec- 

 trical disturbance is a sign of very bad weather. 



As the cyclone approaches the rain increases, and the wind rises 

 into the characteristic squalls of a hurricane. 



The author has been able to find very few signs of any trough 

 phenomena during the passage of a Bengal cyclone. Sometimes a 

 rather sudden shift of wind is described, and a squall with a sudden 

 jump of the barometer, just as is so common in England ; but there 

 does not appear to be the immediate change in the character of the 

 clouds which occurs in these islands. 



Almost all reports agree that the weather is quite as bad in rear 

 as in front of the cyclone ; and the clouds in rear seem to retain their 

 characteristic wild and dirty appearance. The bad weather, how- 

 ever, usually extends much further in front than in rear of the 

 centre. 



Besides these primary cyclones there is another class of small oval 

 depressions, which might either be called primary or secondary, 

 according to the judgment of the meteorologist. 



These form in the Bay of Bengal during the rainy season — from 

 June to September — and though they are much less intense than the 

 storms we have just described, their shape and the rotation of wind 

 round them unmistakeably define their cyclonic nature. The wind 

 round them is never strong; their special characteristic is rain. It 

 has also been observed that they traverse the land and moderate 

 mountain chains without material disturbance of their shape, while 

 the great cyclones are invariably broken up or deflected as soon as 

 their centres touch the coast. 



It has been suggested, with a great deal of probability, that these 

 small cyclones are formed at a higher level in the air than the larger 

 ones. They will not be further considered in this paper. 



The following examples will illustrate these facts. In figs. 2, 3, 

 and 4 we give synoptic charts for India and the Bay of Bengal for the 

 three days May 16 — 18, 1877. These and the extracts from ships' 



