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XVII. Experimental Inquiries relative to the distribution and 
changes of the Magnetic Intensity in ships of war. By George 
Harvey, Esq. Communicated by John Barrow, Esq. F. R. S. 
Read Feb. 26, 1824. 
It having appeared from many unquestionable experiments, 
that the variation of this compass, as determined on ship- 
board, is subject to remarkable anomalies, arising from the 
unequal influence of the iron distributed through the various 
parts of a vessel, and from the changeable intensity of the 
same, occasioned by the different directions of the ship's head, 
with respect to the magnetic meridian, and from its different 
situations on the surface of the earth, it seemed desirable that 
some attempt should be made, to discover in what way the 
attractive forces are distributed throughout the vessel, and 
particularly in the vicinity of the binnacle, by a series of 
careful experiments. 
To trace the variations in the intensity of the magnetic 
forces, under the simplest circumstances possible, the Scylla 
gun brig was selected, having no other iron in her than what 
was necessarily employed in her construction, and for the 
ballast of a ship of her class, when in a state of ordinary. 
The intensity was estimated in planes* parallel to the decks, 
* The term plane has been employed on the ground of convenience. Strictly 
speaking the decks are not planes, but curved surfaces. In the computations rela- 
tive to the position of the centre of force, allowances were made for their variations 
of curvature. 
