distribution, &c. of the magnetic intensity in ships of war. 333 
Of the Ariadne Frigate. 
By permission of Captain Moorsom, who commanded the 
Ariadne, a frigate of 28 guns, the intensity was determined 
at a great number of stations on her different decks. At the 
time the experiments were performed, the vessel lay in a 
complete state of equipment in Hamoaze, having all her guns, 
shot, and other stores on board, preparatory to her departure 
for a long voyage. From her being under sailing orders, it 
was impossible to have her moored in a permanent position ; 
and therefore from the changes which her situation necessa- 
rily underwent, in consequence of the current, one great- 
cause of irregularity, which it is at all times desirous to avoid, 
in an inquiry of this kind, necessarily exercised an influence. 
Some useful information was however obtained from the dif- 
ferent positions assumed by the ship, in consequence of the 
instantaneous and rapid change the magnetic intensity under- 
went at every station. 
The point A in each of the figures contained in Plates. XVII. 
and XVIII., was regarded as the common origin of the three 
co-ordinate planes. The horizontal plane passing through 
IIA2, was assumed at the height of 16 feet 9 inches above 
the plane of the water section QR ; the draught of water 
forward being 13 feet, and abaft 13 feet 9 inches, both di- 
mensions being independent of the false keel. The longitu- 
dinal plane passing through FIAT, was supposed to be 16 feet 
from the middle section, and the tranverse plane £A''F, 
59 feet abaft the centre of the main-mast, on the upper deck. 
The figures denoted by 1, 2, and 3, Plate XVII., represent 
