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Sect. IX. 1 



METEOIiOLOGY. 



30? 



7 



mena as at its coming on. Obsei 



&c., to be continued at gradiially increasing intervals, 

 and at length hourly till the usual state of things is fully 

 restored— gradual rising of clouds at horizon or zenith 

 and banks forming to be noted, and their altitudes mea- 

 sured. The precise position of the ship before and after 

 the gale to be carefully indicated, and all possible infor- 

 mation to be collected of the manner, exact times, &c., in 

 which other ships have been affected by it, a-d every 

 endeavour used to trace out the path of the centre, the 

 diameter of the vortex, and the direction of its revolution, 

 by suT)sequent inquiry whenever opportunity may occur. 



or " cyclones,'* accordin 



Hurricanes, revolving storms, 

 to the meteorologists above named (now fully estabhshed 

 as true representations of fact), differ from mere local and 



of the regular atmospheric 



temporary exaggerations 



currents in this— that they are in the nature of vortices, 

 or circulating movements participated in by masses of 

 air of from 50 to 500 miles in diameter, revolving the 

 more rapidly the nearer the centre, up to a certain dis- 

 tance, or radius, tvithin which there is a calm. The place 

 of this centre of rotation meanwhile advances steadily along 

 a definite line upon the globe, with a velocity varying from 

 2 to 30 or 40 miles per hour, and pursuing a track which 



5 



as 



has a singular fixity of geographical situation and geome- 

 trical form. But the character which it is of most impor- 

 tance to a seaman to know, and the knowledge of whicn 



as 



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has repeatedly been the cause of catastrophes which might 

 have been avoided, is this, viz. :— that in the same hemi- 



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