208 Test of Mr. Espy's Theory. 



this, as in some of the former cases, the field of action of the whirl- 

 wind storm will have been in part mistaken. I would also re- 

 mark, that the points at issue, do not relate to the common and 

 often irregular, winds, which, in different localities, accompany a 

 general fall of rain or snow; or which sometimes attend the pro- 

 gress of a whirlwind storm, exterior to its limits. 



Test of Mr. Espy^s Theory. 



. The truth or error of Mr. Espy's theory may be ascertained by 

 a very simple test. The hurricanes in the West Indies are known 

 to move towards the W. N. W., nearly. Now, if this theory be 

 true, at those islands which are in the centre of the storm's path, 

 and where the gale is of the greatest duration, the wind will set in 

 at about W.N. W., or exactly opposite to the course of the storm, 

 and when its centre has passed over, will shift suddenly to E. S. 

 E., and continue violent in this quarter till the storm is over. But 

 if the gale be a whirlwind, as the facts seem to show, the wind 

 at such places will set in at about N. N. E., and in the middle of 

 the gale will shift nearly to S. S. W., — the wind varying from 

 these points, and veering more gradually, on either side, in propor- 

 tion to the distance from the centre of the storm's track. That 

 this corresponds, mainly, to the facts of the case, will hardly be 

 doubted by those who institute the inquiry. 



The same test may also be applied to these storms as they move 

 in a N. E. direction along the shores of the United States ; where, 

 according to Mr. Espy's views, the gale, on the centre of its path, 

 should blow, for the first part of its duration,, from about N. E. ; 

 and in the second half, from nearly S. W.* But all our inquiries 

 serve to show, that the gale is violent at N.~E. only on the northern 

 portion of the track of the tempest, and that the usual changes 

 from this direction, are not sudden, and to an opposite point of 

 the compass ; but, instead thereof, we observe a gradual veering, 

 by the north, to the northwest. . 



* Some storms, as Mr. Espy has also acknowledged, are interrupted in their de- 

 velopment by the near approach of another storm. Care must be taken, therefore, 

 not to mistake the N. E. wind of a storm whose northwestern limb is thus inter- 

 cepted by a bordering storm, and which hence is sometimes followed by the natural 

 current of air from the S. W. quarter, for the changes that pertain to the centre 

 of the gale. This error is easily avoided by extending the field of inquirj--, and 

 by a due attention to the indications of the barometer. 



