732 Thirteenth Memoir on the Law of Storms in India. [No. 166. 



The consideration of Fig. III. in this point of view, leads I think to a 

 practical result of some, or perhaps much importance ; I consider it thus, 



We see clearly that from X to Y in Fig III. and from x to y in Fig. 

 IV. the whole tendency of the winds was to form a converging spiral, and 

 not a diverging one, or in other words, a circle of which the wind- arrows 

 would turn inwardly and not outwardly.* Now we can have no man- 

 ner of doubt I think that this storm was one of those which, as I have 

 previously shewn, is really the case (See Journal, Vol. IX. Coringa 

 hurricane) was contracting in its progress, and not dilating as many do. 



Is it then the case that, when the storm contracts, the wind forms a con- 

 verging spiral, and e contra if it is a dilating storm, the spiral is a di- 

 verging one ? We are induced to think this highly probable, 'and apart 

 from the great interest of it to the meteorologist, if we find it to be 

 the case, it becomes of high importance to the accuracy of our investi- 

 gations, and moreover to the practical application of the Law of Storms 

 for the purposes of the Mariner ; and it is so from the influence which it 

 has on the true bearing of the centre. 



An example will best shew this. 



If we suppose a contracting storm, i. e. one which has a tendency to 

 diminish in size as it proceeds, of 320 miles in circumference, each arc 

 from point to point of the compass of such a circle will have a chord of 

 something less than ten miles ; across which we may supposed a scud- 

 ding ship to run with one wind till it suddenly or gradually changes 

 to another. But according to the hypothesis that the contracting 

 storms are composed of winds converging to the centre, and not of arcs 

 of a complete circle, we may suppose that each of these thirty-two winds 

 and the corresponding chords of their arcs, which are the ship's courses, 

 are also, not perpendiculars to a radius from the common centre, like true 

 tangents, but to the radii from a succession of centres, which are disposed 

 round the common centre ; in a word, that they converge inwardly also, 

 like the wind- arrows on our charts. 



In the Northern hemisphere they will probably converge inwardly to 

 the left. In the Southern hemisphere to the right? How much do 

 they converge is the next question ? for its reply will give us this datum. 

 The allowance we should make to ascertain the true bearing of the centre 

 in projecting, and even in estimating its position at sea. 



* Our figure approaches to the volute of an Ionic capital. 



