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Sect. XO 



AND BAROMETRIC CURTES. 



333 



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tervals of six hours will be amply sufficient to ascertain 



*.ls, however, on 



its leading barometric phsenomena, 



approaching the continents of North and South America 



or sailing across the equator, should resort to the 



hourly readings, in order to ascertain more distinctly the 

 effect of the neighbourhood of land on the oscillations of 

 the barometer, as generally observed, over so immense a 

 surface of water in the one case, and the phienomena of 

 the equatorial depression in the other : the same remarks 

 relative to the latter subject, which we offered under the 

 head of South Atlantic, will equally apply in the present 

 instance. The configuration of the western shores of 

 North America renders it difficult to determine the precise 

 boundary where the three-hourly series should commence ; 

 the 90th meridian is recommended for the boundary as 

 regards South America, and from this a judgment may be 

 formed as to where the three-hourly observations should 

 commence in reference to North America. 





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In the previous sketch of the localities for the more 

 important observations, it will be seen that within the 

 tropics tliere are three which demand the greatest regard. 



I. The Archipelago between the two Americas, more 

 particularly comprised within the 40th and 1 20th meri- 

 dians west longitude, and the equator and the 40th degi'ee 

 of north latitude. As a general principle wo should say 

 that vessels within this area should observe the barometer 

 every three hours. Its eastern portion includes the lower 

 branches of the storm paths, and on this account is pecu- 

 liarly interesting, especially in a barometric point of 



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