ON ATMOSPHERIC WAVES. 275 



Barometric Obsei'valions reduced to the Level of the Sea, November 184'2. 



M maximum, m mmimum. 

 Examination of Coloured Diagrams. 



Fig. 2, Plate XLIII. — Diagram exhibiting the variations of the barometer at 

 the stations named in the above table, the altitudes reduced to the level of the sea. 

 The depth of each colour indicates the depression of the atmosphere between 

 the terminating stations ; and the intersections of the curves show that at the 

 times of intersection the pressure at each station was the same, and that the 

 relative pressure at these stations became altered, diminishing at one and aug- 

 menting at the other. The progression of the minimum in a line from Dublin 

 to St. Catherine's Point* is very apparent, also the direction of the trough from 

 Scilly to Longstone. The progression of the maximum from Scilly towards 

 Longstone is also exhibited ; namely, Scilly, South Bishop, St. Catherine's 

 Point, Bardsey, Dublin. The general tendency to a level, with the intersec- 

 tion of the curves in the western portion of the area during the last eight 

 hours, is very apparent. 



Fig. 3, Plate XLIII. — Projection of the St. Catherine's, Bardsey and Dublin 

 curves, showing the depth of atmosphere from St. Catherine's to Dublin, and 

 the interchange of level between Dublin and Bardsey. 



These diagrams are intended to exhibit, not only the variations of atmo- 

 spheric pressure at the stations selected, but also those over the area included 

 by them. This area is shown in fig. 1, Plate XLIII. The observations com- 

 mence with a considerable dip from Scilly to Longstone ; the depth of each 

 colour indicates the slope between the two stations bounding it. The form 

 of the atmosphere, Nov. 8.15 hours, between the two extreme stations, Scilly 

 and Longstone, is given by the highest blue curve (a) in fig. 1, Plate XLIV. 

 The trough of the wave A 1 (see remarks on atmospheric waves) passed 

 Dublin about two hours earlier than the recorded minima at the other 



* It is probable from other considerations that the minimum at St. Catherine's Point was 

 occasioned by the passage of the anterior trougli of wave B 1 . 



T 2 



