ON THE METEOROLOGY OF IRELAND. 343 



BAROMETRIC PRESSURE. 



An attempt* was made to correct the barometric results, by a 

 careful comparison of the several instruments with the Dublin 

 standard, by means of portable barometers, and by the reduction 

 of the results to the sea-level, calculated at the rate of '0011 of an 

 inch for each foot of altitude. These results are, however, incom- 

 plete, no comparisons having been made of the barometers at the 

 four inland stations. For this reason, and also because of the 

 uncertainty attending the comparison of barometers by means of 

 portable instruments, I have thought it necessary to seek th 

 corrections by a comparison of the observed results themselves. I 

 comparisons of this kind, where the stations are widely separate; 

 it seems necessary to employ the means of a somewhat extendt 

 series of observed results, during which the fluctuations of bare 

 metric pressure are small. I have accordingly selected for the 

 purpose the monthly means of May, July, and September, in which 

 months there was but little variation of barometric equilibrium. 

 The defects of the means at each station, compared with those at 

 Dublin, for these months, are given in the following Table, and 

 the last column contains the inferred corrections, which are equal 

 to the mean differences + *021, the added number being the reduc- 

 tion of the Dublin results to the sea-level. 



