SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 439 



sort of surface (land, sea, &c.) suffice to determine a value of i, which 

 can tlien be applied to all cases of cyclones of every degree of severity 

 above a surface of the same kind. 



These conclusions agree very well with the results of the investigation 

 •of Clement Ley into the inclination of the wind to the isobars (see this 

 journal, vol. ix, p. 95). The observations at the English stations gave 

 a larger value of i in the interior of the country than on the sea-coast 

 and in the upper regions of the atmosphere. Ley further found that 

 the inclination was the greatest for the ESB. winds, and least for the 

 WNW. winds, while the mean direction of progress of the cyclones was 

 from SW. to !NE. The inclination, therefore, appears greatest in the 

 front portion of the cyclone, where masses of air previously at rest must 

 be first set in motion, and perhaps this is a general law.* It also agrees 

 with the theory that in the interior of a continent the strong winds 

 should have a less inclination to the isobars than the weak ones, and 

 that the inclination is much more constant for strong than for weak 

 winds, for the strongest winds are to be found in the neighborhood of 



the center of a cyclone where — is large in comparison with v n sin <p. 



r 



Professor Loomis found the value of i in the United States under north 

 latitude about 45° much greater than Ley found it for Great Britain 

 under north latitude about 50°. This agrees in general with theory. 

 The somewhat too rapid increase of i is, according to Ferrel, to be 

 ascribed to the greater resistance due to friction in a less cultivated, 

 wooded country. 



The trade wind at a mean latitude of 20° gives an inclination i = 20'^, 

 which is very much greater than Ley found at coast stations in England. 



In tbe case of violent tornadoes and waterspouts, where the rotation 

 takes i)lace very near to the center and with the greatest violence, ti is 

 more important than n sin f, and this term can be entirely neglected, 

 especially in low latitudes. On the other hand, in extensive cyclones and 

 at a considerable distance from the center, n sin ^ is more important than 

 «, and the value of AB depends principally upon the effect of the earth's 

 rotation, and only in slight degree upon the centrifugal force that is 

 called out by the rotation with reference to the earth's surface of the 

 mass of air about the center. 



In the center of a cyclone, the pressure of the air must be a minimum : 

 therefore JB = 0; whence al«o v = 0; and a calm must prevail at the 

 center. 



In large cyclones, up to considerable distances from the center, AB 

 attains no great value, and therefore the calm region must have a con- 

 siderable diameter. In many cyclones, the area of perfect calm attains 

 a diameter of 30 miles. 



In the outer portion of a cyclone, the rotation must necessarily be in 



* But Loomis found tho greater inclination in the rear in the American storms (see 

 this journal, vol. ix, p. 249). 



