332 Dove on the Law of Storms. 



if for this very reason they move from east to west, they will 

 prevail by preference in the eastern part of the Indian Ocean ; 

 and in fact it has been remarked by Dampier that on the coast 

 of Coromandel storms are looked for in April and September, 

 which are the months of the change of the monsoons, whilst on 

 the Malabar coast they are frequent daring the whole westerly 



monsoon. 



Having thus found in the typhoons a confirmation of the prin- 

 ciples which were applied to the West India hurricanes, we may 

 proceed to consider in greater detail the phenomena which ac- 

 company these great disturbances of the atmosphere. 



When in the storms of the regions of the trades the rotating 

 cylinder from the lower trade impinges on the upper current, it 

 is evident that inasmuch as a southwesterly direction of the wind 

 prevails above, the reasoning which has been made use of for 

 the lower part of the same cylinder when it passed beyond the 

 external limit of the trades, becomes applicable to its upper part, 

 which will immediately spread, and will advance in a different 

 direction from that of the lower part of the whirlwind. Thus 

 will arise the secondary phenomenon of suction in the middle of 

 the whirlwind, producing a diminution of pressure on the surface 

 of the earth, and this for two reasons, viz. inasmuch as the rota- 

 tion causes the air to fly from the centre, and as moreover the 

 whirlwind widens conically in ascending, and consequently the 

 upper strata are more distant from the axis of the cylinder than 

 the lower, which have therefore a tendency to ascend in order to 

 compensate the diminished density above. 



But that the storm itself does not originate from this kind of 

 suction, will be evident on a closer consideration of the observa- 

 tions. I will take as an example the hurricane of the 2nd of Au- 

 gust, 1837, for which we have simultaneous observations at St. 

 Thomas and at Porto Rico, which are shown in comparison in 

 the following table : 



