330 



surface, after a lapse of three years or more, of insoluble 

 crystals of carbonate lime, having the form and hardness of 

 calc spar, which prevent chemical action on the metal. 



The Rev. H. Lloyd, V. P., read a paper descriptive of 

 the Magnetical Observatory of Dublin, and of the instru- 

 ments and modes of observation employed there. After 

 some prefatory remarks on the anomalous movements of the 

 magnetic declination, and on the establishment of magnetical 

 stations which took its rise from their study, the author pro- 

 ceeded to the immediate subject of his communication. 



The Magnetical Observatory of Dublin was erected by 

 order of the Board of Trinity College, the funds being sup- 

 plied from the College chest. The building was commenced 

 in the summer of the year 1837, and was completed in the 

 course of the following year. The structure, which is of the 

 Doric order, is situated in an open space in the gardens 

 attached to the College : its dimensions are forty feet in 

 length, by thirty in depth. It is constructed of Portland 

 stone, the interior stone of the building being the argil- 

 laceous limestone (calpe) of the valley of Dublin ; several 

 specimens of each of these stones had been previously sub- 

 mitted to a rigid examination, and found to be entirely 

 devoid of any effect upon the magnetic needle. The interior 

 walls of the building are studded, for the purpose of main- 

 taining a uniform temperature, as well as to protect from 

 damp. The nails employed in the woodwork are of copper, 

 and the other metallic fastenings (locks, hinges, &c.,) of brass; 

 no iron whatever being used in any part of the building. 



The interior is divided into one principal room and two 

 smaller rooms ; one of the latter serving as a closet, and the 

 other as a vestibule. The principal room is thirty-six feet 

 in length, by sixteen in breadth ; and has projections in its 

 longer sides, which increase the breadth of the central part 

 to twenty feet. This room is lighted by a dome light at top, 



