1884.] of the Bay of Bengal in 1883. 181 



In both examples, the greater portion of the mass of air that was thrown 

 into a state of violent motion during the storm was for some days ante- 

 cedent to the disturbances almost at rest, and in a state of approximate 

 equilibrium. There was a break in the rains immediately preceding the 

 formation of the first storm, which is well-known to be a period of light 

 and unsteady winds in Bengal, and over the Head of the Bay. The second 

 storm occurred very shortly after the first break in the north-east mon- 

 soon rains on the Coromandel coast, and when, as the various observations 

 prove, winds were very light and variable over the greater portion of the 

 Bay. Hence the first and most striking feature of these cyclones was, 

 that a vast amount of kinetic energy, or motion, was rapidly given to a 

 large mass of air which, previously to that action, was in an almost quies- 

 cent state. The gradual increase of the motion was in those two examples 

 proved from observations taken by vessels passing through the areas of 

 disturbance. The transformation from the state of approximate quiescence 

 to that of violent cyclonic motion in the Bay is consequently a continu- 

 ous process, the successive stages of which can be fully traced. And the 

 entire development of these, and of all storms in the Bay of Bengal, 

 appears to be due to actions occurring over the Bay itself, and not to 

 atmospheric conditions at a considerable distance from the area of 

 cyclonic disturbance. 



The question of cyclone generation is therefore essentially one of 

 transfer of energy. Viewed in this light there are two subjects for 

 enquiry : — 



1st. The source and character of the energy which is transferred 

 to the atmosphere, and transformed into the kinetic energy of a mass of 

 air. 



2nd. The conditions necessary for the transfer of energy under 

 consideration. 



If these two questions are fully answered, a satisfactory explanation 

 will be given of cyclonic generation as a meteorological problem. The 

 complete mathematical treatment of this subject as a dynamical question 

 is beyond the scope of the present article. 



The energy which is transformed during the generation and exis- 

 tence of a cyclone, and which maintains the cyclonic circulation against 

 the various resistances opposing it, and therefore tending to disinte- 

 grate it, is undoubtedly the latent heat energy given out during the 

 condensation of aqueous vapour contained in the atmosphere. In all 

 cyclones of the Bay of Bengal that have hitherto been investigated, 

 heavy and, in the majority of cases, torrential rain is the most pro- 

 minent feature. It increases in amount during the generation of the 

 cyclone, is excessive during tlie existence of the cyclone iu its complete 

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