distribution, &c. of the magnetic intensity in ships cf war. 331 
136.50; and at O, on the horizontal roof of the sky-light, 
and on which the binnacle rested, it was 100.29? At the 
station F also, the intensity was 118.26; so that a station 
might have been found between the points F and G, at which 
the intensity would have been about 131 ; a fourth propor- 
tional to the two variations above alluded to, and the inten- 
sity at o. The observation also, that the magnitude of the 
difference between the two variations, gradually diminished, 
as the compass on the gangway was brought nearer the 
binnacle, affords a very striking coincidence with the inten- 
sities successively determined at the stations F, E, D, and C; 
they being respectively 118.26, 117.14, 110.35, and 105.20; 
and this analogy was farther confirmed at the station 9, in 
the circumference of the interior circle, nearly midway be- 
tween the stations o and C, the intensity at that point being 
102.87, and at ©, as before mentioned, 100.29. 
The cause of the anomaly in the variation, was considered 
by the officers of the Trent to arise from “ the quantity of 
c< iron stowed round the main-mast, consisting of shot, chain 
“ cable, spare rudder with an iron bolt, and the iron fen- 
“ ders ;” and in the present case, the increased intensity is 
to be attributed to the action of the sheet anchor, which was 
laid across the main hatchway. 
A similar decrease of intensity was also traced from g on 
the larboard gangway to the centre of the binnacle, in a 
manner still more perfect. It may be proper to observe, how- 
ever, that the direction of the Trent's head at the time the 
observations were made was NE ■§• N, whereas the Helicon 
was moored N \ E. 
A case agreeing more exactly as to the position of the 
