324 Mr. Harvey's experimental inquiries relative to the 
her head was north, it was found to be 7.58 feet below it ; 
when east, 7.77 feet, and when north-west, 7.64 feet. The 
depression of the centre of force below this plane is therefore 
the least when the ship's head is north, and the greatest when 
due east ; the distance in the north-west position being nearly 
a mean between the two. 
Hence it appears that the motion of the centre of force, is 
in that species of line which geometers denominate a curve 
of double curvature . 
For the sake of practical reference it may be added, that 
the position of the centre of force when the ship’s head is 
north, is nearly in the middle section, at the foremost part of 
the main hatch- way, and about ten inches and a half below 
the upper surface of the upper deck. 
Of the Helicon . 
The next vessel selected was the Helicon brig, mounting 
ten guns, and in a complete state of equipment for sea. On 
applying to Captain Dawkins, her commander, he immedi- 
ately caused her to be moored with her principal section in 
the direction of the magnetic meridian. 
The first line of stations assumed was in the middle sec- 
tion of the ship, in which however only six points, a, / 3 , 7, 
s, J, fig. 2, Plate XIX., could be obtained, on account of the 
midship part of the deck, from the main hatch-way, forward, 
being occupied by an anchor, boat, ship’s gear, &c. On the 
starboard and larboard sides, at the distance of five feet from 
the middle section, two other sections were assumed, in which 
