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326 



ON ATMOSPHERIC WAVES 



[Sect. X. 



that off the nortli-west of vScotland a centre of great 

 barometric disturbance exists. This centre of disturbance 

 appears to be considerably removed from the usual tracks 

 of vessels crossing the Atlantic ; nevertheless some light 

 may be thrown on the barometric phsenomena resultino" 

 from this disturbance by observations during homeward- 

 bound voyageSj especially after the vessels have passed the 



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meridian of 50 

 Baffin and Hud 



west longitude 



Voyagers to or from 



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of the voyage to read off the barometer every three hours, 

 as their tracks would approach nearest the centre of dis- 

 turbance in question. Before crossing the 50th meridian, 



the undulations arising from the distribution of land and 



water m the uei'jiibourhood of these vast inland seas 

 w^ould receive considerable elucidation from the shorter 



intervals of observation, and after passing the 50th meridian 



the extent of undulation, as compared with that observed 

 by the more southerly vessels, would be more distinctly 

 marked by the three-hourlv series. Surveying vrreh 



coasts of Ireland and 



stationed on the north-western 

 Scotland may contribute most important information on 

 this head by a regular, and as far as circumstances will 

 allow, an uninterrupted series cither of six-hourly or 

 three-hourly ol.servations. The intervals of observation 

 on board vessels stationed at the Western Isles, the 

 Orkneys, and the Shetland Isles, ought not to be longer 

 than three hours, principally on account of the great ex- 

 tent of oscillation observed in those localities. Vessels 

 arriving from all parts of the world as they approach the 

 United Kingdom should observe at shorter intervals than 

 IX hours. As a general instruction on this head the 



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