t 



f 



Sect. X.] 



AND BAROMETRIC CURVES. 



825 



•V' 



r^ 



K 



J 

 . I 



, 1 



1 c*1 



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■o 



apprehended. It need scarcely be said that the value of 

 these observations at three-hourly intervals will be greatly 

 increased by the number of observers co-operating in 

 them. Upon such an extensive system of co-operation a 

 large space on the earth's surface, possessing peculiarities 

 wliich distinguish it from others extremely unlike it in 

 their general character, or assimilate it to such as possess 

 with it many features in common, is marked out heiow 

 for particular observation, occupying more than two-tiurds 

 of a zone in the northern hemisphere, having a breadth of 

 40", and including every possible variety of terrestrial 

 and aqueous surface, from the burning sands of the great 

 African desert, situated about the centre-, to the narrow 

 strip of land connecting the two Americas on the one side, 

 and the chain of islands connecting China and Hindostan 

 with Australia on the other. On each side of the African 

 continent we have spaces of open sea between 30'' and 

 40^ west longitude north of the equator, and between 60' 

 and 80^ east longitude, in or to the south of the equator, 

 admirably suited for contrasting the barometric affections, 

 as manifested in these spaces of open water, with those 

 occurring in situations where the influence of the terrestrial 

 surface comes into more active operation. 



The localities where three-hourly readings are chiefly 

 desirable may be specified under the heads of Northern 

 Atlantic, Southern Atlantic, Indian and Southern Ocean 



^\ 



Paciji 



*5 



Noriheru Atlantic. Homeward-hound Voyages. —The. 

 discussion of observations made in the United Kingdom 

 and the western border of central Europe, has indicated 



