in the Air and in the Sea, 179 



have been regarded as the basis of meteorology, or as currents 

 on which all the movements of the air depend. To this opinion 

 we cannot assent ; on the contrary, we believe that in the atmo- 

 sphere, just as in the sea, the principal motions take place in 

 directions nearly parallel to the equator. 



Perhaps, in the future, with more accurate knowledge of the 

 action called forth by the attractions of the sun and moon, we 

 shall succeed in explaining the causes of rotatory storms by the 

 two opposite directions of the flood- and ebb-current. May 

 not in certain cases, at the time of the quadratures, the ebb-cur- 

 rent caused by the moon meet at a certain angle the flood-cur- 

 rent called forth by the sun and thereby produce the rotating 

 motion ? Up to the present time the important natural pheno- 

 menon of cyclones has by no means been explained ; for all 

 hitherto-given explanations have been quite inadequate. 



As is known, these storms always have two motions — one 

 rotating^ and one progressive. The progressive motion corre- 

 sponds well with the theory of the moon's attraction ; for these 

 storms almost always commence in low latitudes, and, in both 

 hemispheres, the centre of the storm moves westward in the 

 region of the flood-current, at the same time slightly increasing 

 its distance from the equator and thereby arriving in the calm- 

 zone of the tropic. Here the velocity of the progressive motion 

 becomes considerably less, and its course makes a sharp curve 

 eastward, the hurricane passing into the region of the ebb-cur- 

 rent ; and now, in both hemispheres, it moves with great velo- 

 city to the east and somewhat polewards. Therewith its dia- 

 meter gradually increases and the circular motion diminishes 

 until the hurricane is lost in higher latitudes. The usual dura- 

 tion, from beginning to end, of the hurricane is about 14 days. 



The rotating motion of these storms is subject to quite deter- 

 minate but not yet discovered laws. In the northern hemisphere 

 they rotate in the opposite direction to that of the hands of a 

 clock ; but in the southern hemisphere they go round in the 

 same direction as the latter. In other words, in both hemi- 

 spheres the storm always blows from the west on the side to- 

 wards the equator, and from the east on the polar side. West- 

 wards of the centre of the hurricane, the direction of the storm 

 is always to the equator ; eastward of the centre, away from the 

 equator; so that hurricanes rotate in an opposite direction to 

 the currents of the seas. Ordinary storms appear to stand in 

 the closest connexion with cyclones; at least this conjecture is 

 corroborated by Buys-Ballot's law, according to which the winds 

 revolve about the minimum of atmospheric pressure in the same 

 direction as the cyclones. 



The explanation that the rotating motion of cyclones arises 



N 2 



