274 REPORT — 1844. 



(22.) Nov. 9.17.0. — A maximum passes Dublin. This is most probably 

 the apex of wave A 2.* The posterior minimum of A 1, or anterior minimum 

 of A 2, passed this station Nov.9.1.0, and the anterior minimum of B 1 did 

 not pass Scilly until Nov. 9.3. The rise at Dublin, South Bishop, Bardsey 

 and Longstone must have been occasioned by the anterior slopes of A 2 and 

 B 1 combined ; but more light will be obtained on these points by a discussion 

 of the curves of the remaining stations, 



(23.) Nov. 9.18 and 19. — Scilly, South Bishop, Banlsey and Longstone 

 nearly on a level. The barometer descending at the three first-named stations 

 and rising at Longstone, indicates that the apex of the wave was passing be- 

 tween Longstone and Bardsey. The coloured diagram exhibits a considerable 

 depth of atmosphere from St. Catherine's Point to Bardsey, and a rise from 

 Bardsey to Dublin, showing that the trougli of A 1 is still between the ex- 

 treme stations, or that it has not been sufficiently deep to depress St. Cathe- 

 rine's Point below Bardsey. This, however, with several other interesting 

 points, will be fully elucidated in the further discussion. 



(24.) The characters of the two waves A 1 and B 1 (or rather three, in- 

 cluding A 2), as developed in the foregoing inquiry, support, I apprehend, 

 the idea of a permanent slope from Scilly to Longstone. The waves B 1 and 

 A 2 appear to have been nearly of the same altitude, or to have exerted 

 nearly the same pressure in their passage. The curves due to their combined 

 action in the south of England are small : these curves increase towards the 

 north. Longstone, which exhibits the least pressure during the period of 

 these observations, developes the largest curve ; and at this station a consi- 

 derable rise is due to the passage of A 2. This must necessarily take place 

 at a station situated as Longstone appears to be, — in a valUe atmospheriquef. 



* The superiority of the Dublin to the Bardsey curve, for some hours subsequent to this 

 epoch, indicates that this maximum was due to the apex of B 1. 



t Since this paragrapli was written, I have inserted in Plate XLIV., fig. 1, the curves exhibit- 

 ing the distribution of pressure on the line from Scilly to Longstone for the epochs Nov. 10.3 

 and 10.9 (see curves g and ft). These curves very clearly indicate the precise characters of 

 the waves A 1 and B 1, and when we combine them with the synchronous curves at these 

 stations, we at once see that both A 1 and B 1 were small waves riding on others of a much 

 greater magnitude. The curv es b and c, fig. 1, Plate XLIV., exhibit a slope on which B 1 rolled. 

 (See 5 and 7.) The coloured diagram at the epochs Nov. 8.21 and 9.3 also shows a very 

 considerable fall from Scilly to Longstone. Now as Scilly exhibited the greatest and Long- 

 stone the least pressure, it is clear that these stations were situated under X.\\S anterior slope 

 of the larger wave during the continuance of these conditions, provided such wave was 

 rao\-ing in the same direction as B 1 . When the apex passed between Scilly and Longstone 

 x\\t\x synchronous curves intersected (see fig. 2, Plate XLIIL, about 18 h. 30m. of Nov. 9). Im- 

 mediately afterthe intersection Longstone became the superior curve, and upon the apex passing 

 Longstone the preAious conditions were changed, and both these stations were then situated 

 under t\\e posterior slope of the larger wave. The curves b and c, fig. 1, Plate XLIV., exhibit 

 that portion of the slope in advance of B 1. The curve e of the same figure exhibits B 1 riding 

 on the apex of this wave, and the curves g and h show its posterior slope, which succeeded 

 B 1. By selecting two curves, b and g for instance, the change in the distribution of pressure 

 on this line resulting from the passage of the larger wave is clearly apparent. The gi-oup of 

 curves affords an illustration of a nodal point on a small scale, — the great extent of oscilla- 

 tion at Scilly, its gradual diminution towards and past Bardsey, its small amount at the point 

 n between Bardsey and Longstone, and its augmentation (compared with this point) at 

 Longstone, are interesting illustrations of the increase of oscillation noticed in Sir John 

 Herschel's ' Report on Meteorological Reductions' (Report, 1843, p. 85), which are here 

 clearly seen to result ft-om the passages of the anterior and posterior slopes of a large wave 

 between the transits of its anterior and posterior troughs, n being the nodal point iu which 

 the curves representing the anterior and posterior slopes intersect. 



The following table exhibits the depression of Longstone lielow Scilly during a portion of 

 the transit of the anterior slope of the larger wave, and the depression of Scilly below Long- 

 stone during the transit of its posterior slope : — 



