74 



IV. Results of Observations made at the Magnetical Observatory of Dublin, 



during the Years 1840-43. By the Rev. Humpheey Lloyd, D. D., 

 President ; F. R. S.; Hon. F. R. S. E.; Corresponding Member of the Royal 

 Society of Sciences at Gottingen; Honorary Member of the Anwrican Philoso- 

 phical Society, of the Batavian Society of Sciences, and of the Society of Sciences 

 of the Canton de Vaud, ^c. 



Read May 11 and 25, 1846. 



FIRST SERIES. — MAGNETIC DECLINATION. 



1. 1 HE observations at stated hours, in the Magnetical Observatory of Dublin, 

 commenced in November, 1838, and were at first taken twelve times during the 

 day. Throughout the greater part of the following year, they were made at 

 least eight times daily, with some variations as to the precise hoiurs ; and, at the 

 beginning of the year 1840, the niunber of assistant observers was increased 

 to three, and the observations were made every alternate hour, night and day, 

 according to the comprehensive scheme recommended by the Council of the 

 Royal Society, and followed at more than thirty observing stations in various 

 parts of the globe. This plan has been in operation at the Dublin Magnetical 

 Observatory until the end of the year 1843, when it was discontinued ; four 

 years' observations having been found sufiicient for the determination of all the 

 phenomena connected with the diurnal changes. The observations have been 

 since continued upon a different and reduced scale, and with a view to other 

 classes of phenomena. 



I shall not, in this place, enter into any accovmt of the iastnunents, or 

 methods of observation, as these will be fully explained in the pubhcation in 

 which the observations themselves are presented in detail. I desire merely to 



