Local Attraction of the Steam-vessel Comet 289 
if, on the other hand, it did not amount to so much, then the 
effect would remain the same in quality, but would be diminish^ 
ed in quantity. 
Steam-vessels present nearly a similar arrangement ; the iron- 
chimney standing in place of the mast, and the boiler and en- 
gine in lieu of the usual iron-tanks, ballast, and guns. There 
was also here another question. I had determined, by a long 
series of experiments, that iron, when hot, had a much greater 
power than when it was cold, in many cases more than three 
times ; and it might therefore be presumed, that as, in a steam- 
vessel, most of the iron is kept under a considerable degree of 
heat, the power of this on the compass would be much more 
strong than in ships of the usual kind. 
The following are the principal dimensions of the vessel, &c. 
as they relate to the following experiments : 
Ft. 
In. 
Length of the vessel, 
115 
0 
Greatest breadth. 
21 
0 
Burden, - , , 237 tons. 
Length of boilers. 
15 
0 
Mean breadth. 
15 
0 
Depth, - - - 
8 
6 
Thickness of metal. 
0 
Of 
Height of the smoke-chimney. 
36 
0 
Diameter of do. for 3 feet 3 inches. 
2 
9 
Do. do. for 32 feet 9 inches. 
1 
6 
Thickness, „ - , 
0 
Of. 
Height of steam-chimney, 
25 
6 
Diameter do. - - - 
0 
6 
Thickness, - - - 
0 
The three compass stations are thus distinguished : Binnacle 
compass A, standard compass B, the compass fixed forwards C. 
Compass A near the wheel. 
From A to B was 
From B to C, 
From C to edge of boiler, 
From C to large chimney, 
7 ft. 8 in. 
20 6 
9 0 
15 8 
The vessel was ready for the experiment on the 26th of June^ 
and Mr Lecount, Admiralty midshipman, author of a highly 
ingenious work on the Polarisation of Iron,” having been or- 
dered to go out in her to assist Dr Tiarks in bis experiments. 
