ON THE METEOROLOGY OF IRELAND. 327 



From the preceding Table we obtain the following corrections, 

 which are to be applied to the means of the observed temperatures 

 at 9 A.M. and 9 P.M., in order to reduce them to the mean of 

 the day : 



April, . . corr. = + 0'l 

 May, . * : +0-1 

 June, . . -0-1 

 July, . . +0-1 

 August, . 0-0 



+ 0-2 



October, . . corr. = + 0'5 



November, . + '7 



December, . + '6 



January, . . + '7 



February, . +0'6 



March, . . + -5 



It hence appears that the correction is nearly constant through- 

 out the summer, and throughout the winter months, respectively. 

 The mean summer correction is + 0'l ; the mean winter correction 

 + 0-6. 



Mean Monthly Temperatures. The mean temperatures have been 

 obtained, at all but three of the stations, from the observations at 

 9 A.M. and 9 P.M., by the application of the preceding corrections. 

 At Markree the observations were taken at 10 A.M. and 10 P.M. ; 

 and the reducing numbers are therefore somewhat different, and 

 smaller in amount. At Portarlington and Athy the observations 

 were taken but once in the day, namely, at 9 A. M. ; and at these 

 stations, accordingly, the mean temperatures are inferred from the 

 maximum and minimum temperatures, as given by the self-regis- 

 tering thermometers. The formula employed is that of Kromtz, 

 viz. : 



mean temp. = min + a (max. - mi>i.) 



The mean value of the coefficient,* as deduced from the observa- 

 tions at the observatories of Armagh, Markree, and Dublin, is 

 a = 0-41. 



The following Table contains the resulting values of the mean 

 temperature for the several months of the year 1851 : 



The coefficient in Ksemtz's formula appears to vary considerably at different 

 places, both in its -mean amount, and in the law of its variation from month to month. 

 At Armagh and Markree its greatest value is in December, and ite least in July ; at 

 Dublin, it is the reverse. I have taken above the mean of the yearly values for the 



three stations. 



