Tropical and Extra-tropical Cyclones. 



7 



this is quite different from the central calm and blue sky of a tropical 

 hurricane. Though he cannot say that a clear-centre cyclone never 

 occurs in this country, it is perfectly certain that the phenomenon is 

 very rare. 



Indian Cyclones. 



Attention will now be directed to Indian cyclones. 



The result of the author's investigations, both of the published 

 records of the various Indian meteorological departments and from 

 verbal communications, gives the following as the general character 

 of Indian cyclones. 



The shape is usually oval ; but the side towards which the isobars 

 are pressed, and the consequent lie of the longer diameter, varies 

 much, even in the same cyclone on different days. 



The diameter is smaller than in the Atlantic ; but pressure 

 diminishes much more rapidly near the centre than in Europe, though 

 the actual minimum need not be very low. 



The general surroundings, the formation, development and dissipa- 

 tion of cyclones seem to be essentially the same as in Europe. There 

 are two types of cyclones in the Bay of Bengal. Those in May are 

 associated with the breaking up of a belt of high pressure, in a manner 

 to which we find many analogies in Great Britain ; while those in 

 October are formed in a general depression over the Bay, exactly 

 analogous to the commonest conditions of cyclone formation in the 

 Atlantic. 



Secondaries sometimes form on the side of the primary cyclone, 

 but not nearly so often as in the temperate zone. 



The motion of the cyclone is almost invariably towards the N.N.W. 

 or 1ST.W. at first, with a marked tendency to recurve towards the N". 

 and N.E. later on. 



The velocity of translation is much less than in Europe, varying 

 from about 3 to 20 miles an hour. 



The rotation of the wind is always in an in-going spiral ; but there 

 does not seem to be any marked tendency to greater or less incur- 

 vature in any particular quadrant of the cyclone. The violence of 

 the wind seems to increase as the centre is approached, which is not 

 the case in the British Isles. 



The author does not think that there is sufficient evidence for the 

 assertion that the centre of wind rotation is not coincident with the 

 barometric centre of the cyclone. In the cases that have been 

 reported on board ship, which he has investigated, he is unable from 

 the materials at his disposal to separate the barometric change due to 

 the motion of the ship in her course from that due to the motion of 

 the cyclone. 



For instance, if a ship were motionless, and a cyclone passed over 



