ON THE METEOROLOGY OF IRELAND. ,371 



appear to increase with the distance from a line or axis of minimum 

 pressure, rather than from a point ; or, in other words, that the 

 iwbaric lines are parallel right lines, instead of concentric circles. 

 It is true that these facts are by no means decisive in disproving 

 rotatory movement ; for they are consistent with a rotation of the 

 wind in a plane perpendicular, or highly inclined, to the horizon. 

 Still we are perhaps not justified in assuming the existence of a 

 rotation of this kind, without further evidence ; and it seems more 

 reasonable, in the present state of our knowledge, to admit two dif- 

 ferent kinds of winds, than to endeavour to reduce all to one by 

 the help of a gratuitous hypothesis. 



Hourly Observations. It has been already stated, that hourly 

 observations were appointed to be made during twenty- four conse- 

 cutive hours, at the equinoxes and solstices, in the hope that their 

 results might throw light upon the simultaneous atmospheric 

 changes occurring over the island, and especially upon the direc- 

 tion and rate of progress of atmospheric waves. The results of the 

 observations on the first two of these term-days March 21, and 

 June 21 are here given. During the two latter September 22 

 jmd December 22 no atmospheric change of a marked kind 

 occurred. 



March 21. A gale occurred on this day, accompanied by a 

 marked barometric depression. The minimum of pressure took 

 place during the observations, the time of its occurrence varying 

 considerably at the different stations. At Cahirciveen, there was 

 a sudden fall of the barometer between 9 A. M. and 10 A. M., fol- 

 lowed by a sudden rise between 12 and 1 P. M., the mercury being 

 nearly stationary from 10 A. M. to 12. A similar change took 

 place at Dunmore East, and at the same hours. For these two 

 stations, accordingly, the epoch of minimum pressure may be taken 

 to be 11 A.M. ; the subsequent changes were small and irregular. 

 At Courtown, the barometer descended very slowly and gradually 

 until 5 p. M. ; it then ascended until 10 p. M., after which it de- 

 scended again. All the changes were, however, very small. 



At the northern stations the fall of the barometer was more 

 considerable, and more regular. At Markree, where it was most 

 rapid, it amounted to 0*210 in 6 hours. The minimum at Markree 

 occurred between 3 P. M. and 4 P. M. ; at Armagh, the minimum 

 took place at 6 p. M. ; and at Portrush, at 8 p. M. 



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