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, 
