ON THE METEOROLOGY OF IRELAND. 323 



The instruments were furnished by the Academy to the Coast- 

 guard and Light-house stations, and were constructed under the 

 direction of the Council, and upon a common plan. They consist of 

 a barometer ; a pair of ordinary thermometers (dry and wet bulb) ; 

 a pair of self-registering thermometers; a wind- vane; Lind's 

 anemometer; a rain-gauge; and (at the Coast-guard stations) 

 a thermometer adapted to the observation of sea temperature. 

 The thermometers were previously compared in Dublin with the 

 standards belonging to the Magnetical Observatory, and their 

 errors exactly determined. The barometers were compared with 

 the Dublin standard, after they were placed at the several stations, 

 by means of good portable barometers ; and the heights of the 

 cisterns above the sea were ascertained by levelling. All this was 

 done by members of the Council, under whose superintendence the 

 instruments were erected. 



The four thermometers at every station were inclosed in a 

 shallow box with a sloping roof, and wire-gauze front. A vertical 

 gnomon was fixed at most of the stations in the window-sill of the 

 guard-house, for the purpose of determining the time of noon ; and 

 the observers were furnished with a Table of the equation of time, 

 computed for the year 1851, and for the mean longitude of Ireland. 

 The barometers were put up, generally, in the guard-house of the 

 station. 



Plan of Observation. It is probable that over a tract of country 

 so limited as this island, the distribution of temperature, humidity, 

 and rain, does not vary materially from one year to another ; and 

 that, consequently, a tolerable approximation to the laws of this 

 distribution may be obtained from the results of a single year, if 

 every precaution be adopted to insure the perfect comparability of 

 the results. It was arranged, accordingly, that the observations 

 should be coijtinued at the Coast-guard stations until the end of the 

 year 1851, so as to embrace a period of at least one year, reckon. -.1 

 from the time when the observers had acquired the power of ob- 

 serving with accuracy. The monthly means for this year may be 

 reduced to their absolute mean values, by the help of the more 

 extended series of observations made in Dublin, by which the 

 deviations of any monthly result from its absolute mean value 

 is sufficiently known. 



The Committee, upon whom the duty of superintending these 



