372 ON THE METEOROLOGY OF IRELAND. 



From these results it would appear that the trough of the wave 

 travelled from south to north, nearly, with a velocity of about 22 

 miles per hour. The barometric depression was greatest at Markree, 

 where the barometer stood at 28'689, when lowest. The lowest 

 pressure increased from that point in the south-easterly direction, 

 being 28-972 at Dunmore. 



At Markree the wind shifted from S. S. E. to S. S. "W. at the 

 time of greatest depression. The same phenomenon took place at 

 Armagh and Portrush, although not with such precision; the 

 change of direction at the former station being from S. S. E. to S., 

 and at the latter from S. E. to S. No similar change occurred at 

 the southern stations. 



The foregoing phenomena are not necessarily to be ascribed to 

 the transit of a rectilinear wave. They are all consistent with the 

 effects of a cyclone, coming from the S. or S. W., the track of its 

 centre lying to the west of the island. 



June 21, 22. The changes of the direction and of the pressure 

 of the wind, on these days, are manifestly the effects of a cyclonic 

 movement, the centre of the vortex sweeping round the north coast 

 of Ireland, in a somewhat curvilinear path, from west to east. It 

 has not been included in the former series, the force of the wind 

 having been below the limit there adopted. At 9 A. M. of the 21st, 

 the centre of the vortex was off the north-west coast, to the west 

 of Killybegs. At 9 p. M. of the same day it had arrived to the 

 north of Portrush ; and at 9 A. M. of the 22nd it was to the north- 

 east of Donaghadee. 



The veering of the wind was, on the average, about 90; its 

 duration was very different at the different stations, being shortest 

 for those near the path of the centre of the vortex, and longest for- 

 t-hose remote. The wind, which was very light throughout, fell 

 about the time of veering at most of the stations. 



The descent and subsequent rise of the barometer were regular, 

 and the minimum well-defined. The time of least pressure coin- 

 cided at all the stations, very nearly, with the middle of the time 

 of veering of the wind ; it was earliest on the western coast, and 

 latest on the eastern, the epoch of its occurrence being between 12 

 and 1 P. M. at Markree and Cahirciveen, and between 5 p. M. and 

 6 p. M. at Dublin and Courtown. The barometric depression was 

 small, the mean pressure at the epoch of minimum being 29 '74. 



