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Art. V. A popular View of Mr Barlow s Magnetical 
Experiments and Discoveries , particularly as they have been 
rendered applicable to the Correction of the Local Attraction 
of Vessels. 
Several detached notices of Mr Barlow's experiments and 
results, have been given in some of the preceding volumes of 
this Journal ; but the great importance of them to nautical 
science, has been lately so strikingly demonstrated by a Report 
of the Author's, addressed to the Admiralty, detailing a series of 
experiments made, by order of that Board, in his Majesty's 
vessels in various parts of the globe, that they now possess a 
new and more general interest ; and we feel assured, that a con- 
nected and popular view of the whole subject will be acceptable 
to our readers in every part of Europe. 
Of the numerous interesting facts with which philosophy has 
been from time to time enriched, by far the greater number 
may be traced to some fortuitous or accidental circumstance ; 
and it belongs perhaps almost exclusively to the nineteenth cen- 
tury, to boast of some valuable discoveries, which, independent 
of chance, have resulted from scientific investigations and expe- 
riments directed to a specific object : Of these, the safety-lamp 
of Sir H. Davy, and his present chemicc-electric guard to the 
copper of vessels, and the correcting plate of Professor Barlow, 
form memorable examples ; and in all these cases, the value of 
the discovery is only equalled by the extreme simplicity of the 
application. 
It is now at least 600 years since the compass began to be em- 
ployed as a nautical instrument ; and yet it is only within a short 
period, that an imperfection has been discovered in it, which de- 
tracts much from its real value for such a purpose, namely, that 
the needle does not continue to point in the same direction, with 
the ship's head at different points, the difference in some cases 
being so great as to lead to the most fearful errors and uncer- 
tainties. The general nature of this effect will be understood, 
by considering, that the upper parts of all iron bodies attract 
that end of the needle, which, when freely suspended, dips below 
the horizon, that is, the north end in the northern, and the south 
VOL. XI. NO. SI. JULY 1824. 
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