328 



Dove on the Law of Storms. 



Fig. 3. 



gust, 1830, was much slower in its progress. It began in lat. 

 20°, to the north of Porto Rico, and preserving about the same 

 distance from the coast of North America, reached the banks of 

 Newfoundland on the 27th.* 



The explanation of these phenomena appears to be the fol- 

 lowing : — 



Let a b (Fig. 3.) be con- 

 sidered to represent a series 

 of material points parallel to 

 the equator ; supposing these 

 points to receive from any 

 cause whatever an impulse 

 in the direction a c towards 

 the north, then, inasmuch 

 as they would be transferred from greater to lesser parallels of 

 latitude, they would move towards g h if the space d b h were 

 a vacuum ; but if there be in this space air not in movement, 

 then the particles in 6, as they move towards d, will be continu- 

 ally coming in contact, in the space d b h, with particles of air of 

 inferior rotatory velocity, and thus their own eastward velocity 

 will be diminished. Thus the point b will move towards/in- 

 stead of towards h; but the particles at a have near them, on the 

 side of 6, particles of originally equal rotatory velocity with their 

 own ; they move therefore as they would do in vacuo, i. e. to- 

 wards g. Therefore if a b be a mass of air impelled from the 

 south towards the north, then the direction in which the storm is 

 blowing will be much more southerly on its eastern side than on 

 its western side, where it will be more westerly, and thus there 

 will arise a tendency to rotate in the sense S. E. N. W. This 



* As the direction in which the storm is advancing is quite a different thing from 

 the direction in which the rotating current may be blowing at a given place, it is 

 easy to see what incorrect conclusions might be arrived at by an exclusive consid- 

 eration of observations merely local. Thus Raynal in his Histoire Pliilosophique 

 et Politique des deux Indes, Vol. V, p. 72, says that recent observers had noticed 

 that the storms which had ravaged the Antilles from time to time had alwayscome 

 from the northwest, from which he concludes that they came from the mountains 

 of Santa Martha, although all that is really indicated is that the islands are situated 

 on the southern side of a rotating storm, in which, the movement is in the oppo- 

 site sense to that of the hands of a watch, or from east to west, which agrees per- 

 fectly with the observations referred to above. The frontispiece of the sixth vol- 

 ume of Raynal's work is a vivid picture of a West India hurricane. 



