76 



The Rev. H. Lloyd on the Results of Obsei'vations made at the 



obtained on days of disturbance have been omitted, — those being defined to be 

 days of disturbance, in which the sum of the differences between the separate 

 results, and the monthly means corresponding to the same hours, exceeds a certain 

 limit, which is about the double of its mean value. The number of separate 

 observations actually combined, in deducing the monthly means for each hour, is, 

 on the average, 86. The total nimiber of observations employed exceeds 12,000. 

 3. The hours of observation, in accordance with the instructions of the 

 Council of the Royal Society, were the even hours of Gottingen mean time. 

 This being l* 4"" 50' in advance of Dublin time, the observation hours are, 

 nearly, the odd hours of Dublin mean time. The following are the differences 

 of the monthly mean results corresponding to each hour, and the mean of the 

 twelve, expressed in minutes. The positive numbers correspond to easterly 

 deviations of the north pole of the magnet, and the negative to westerly. 



Table I. Diurnal Variation of the Magnetic Declination. 



4. The general features of the phenomenon, as deduced from these numbers, 

 are the following ; 



I. Between 6 A. m. and 8 a. m. (the time varying with the season) the north 

 pole of the magnet begins to move westward, and, therefore, the westerly decli- 



