Experiments and Discoveries. ui 
ether ; yet these compasses, when compared on board the same 
ship, will agree exactly.” 
A few years after this, the action of* the iron of the vessel was 
more minutely noticed by Captain Flinders, who was the first 
to trace its connection with the dip of the needle, and to point 
out that the effect was different in quality on the contrary sides 
of the magnetic equator, and increasing in quantity as the dip 
in either hemisphere increased ; and by him the subject was 
brought under the notice of the Admiralty Board, who ordered 
C5 ^ 
experiments to be made in different ships, in order to ascertain 
the general amount of the error thus produced. r lhe inquiry 
was, however, again lost sight of, till Mr Bain published his va- 
luable treatise on the 44 Variations of the Compass,” in which 
the fatal consequences attending this source of error, are put in 
so clear a point of view, as to strike the most indifferent and un- 
informed readers; and whatever advances have since been made 
towards correction, the nautical profession will owe much of it 
to observations contained in this useful work. It happened, 
that, at this time, our arctic expeditions were in contemplation ; 
and the local attraction of the vessels in those seas, was one of 
the objects to which the attention of the officers was particular- 
ly directed. The results of the experiments made in these in- 
stances, are given by Captains Boss and Parry, in the accounts 
of their respective voyages ; and the amount of the disturbing 
force was found to be such, as to call for some prompt and effi- 
cient remedy, the difference of the bearing of an object having- 
been found by Captain Sabine to be at least 50°, merely from a 
change of position of the ship's head from east to west. 
When the great amount of this error is thus pointed out, it 
will seem extraordinary that it should have remained so long un- 
noticed. It may, therefore, be proper to observe, in justice to 
the memory of the many excellent navigators, whose names and 
discoveries now only live in history, that this effect was much 
less formerly than it is at present, in proportion as the quantity 
of iron used in the construction and equipment of vessels was 
less than at this time. It is only within a few years that pig- 
iron has been employed for ballast, the weight of which, in some 
vessels, exceeds three hundred tons ; an immense surface of iron 
is also introduced, by the admirable invention of iron-tanks, to 
