ON THE METEOROLOGY OF IRELAND. 329 



Before we proceed to discuss the mean temperatures in the 

 several months of the year 1851, it is important that we should 

 know the absolute mean temperatures at some one station, and 

 thereby the deviations from the means in the several months of the 

 year in question. Over a tract of country so limited as Ireland, 

 these deviations, will not differ much in different localities ; and 

 therefore, knowing them for one station, we are enabled to reduce 

 the results of the single year, with probably sufficient exactness, to 

 their absolute mean values at all the rest. 



The absolute mean temperatures of the several months are 

 known, at Dublin, by means of the series of observations made 

 during twelve years at the Magnetical Observatory. The monthly 

 mean temperatures, deduced from that series, are given in the fol- 

 lowing Table. From the year 1840 to 1843, inclusive, the daily 

 means are those of twelve equidistant hours ; from 1844 to 1850, 

 inclusive, they are inferred from the temperatures observed at 

 10 A.M. and 10 P.M. ; and in 1851, from those at 9 A.M. and 

 9 p. M. In the last line of the Table are given the deviations of 

 the monthly means in 1851, from the mean monthly means, as 

 deduced from the twelve years. 



It will be seen from the Table, that the temperature in the 

 months of January, February, and October, 1851, was higher than 

 the average temperature, while, in November, it was considerably 

 lower. The mean temperature of the entire year was only 0-3 

 above the average. 



The depression of temperature in the month of November is a 

 remarkable case of those non-periodic fluctuations to which the at- 

 tention of meteorologists has been drawn by Professor Dove. This 

 fluctuation appears to have proceeded from north-east to south- 

 west, and to have been nearly obliterated when it reached the 

 western coast of the island. At the northern and eastern stations the 

 unusual cold began on the 24th day of the month ; at the southern 

 and western it commenced on the 26th and 27th. It reached its 

 maximum about the 30th, and ceased about the 3rd of December. 

 When we compare the mean temperatures of November and De- 

 cember at Killough, Dublin, Courtown, and Dunmore, on the 

 eastern coast, with those at Killybegs, Westport, Kilrush, and 

 Cahirciveen, on the western, we observe that the temperature of 

 November is less than that of December by 3"'3 at the former 

 stations, while the defect is only 0"-6 at the latter. 



