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VI. On the anomaly in the variation of the magnetic needle as ob- 
served on ship-board. By William Scoresby,^?^. Esq. Com- 
municated by the Right Hon. Sir Joseph Banks, Bart. G. C. B. 
P. R. S. 
Read February 4, 1819. 
The anomalies discovered in magnetical observations con- 
ducted on ship-board, were usually attributed to the imper- 
fection of the azimuth compass, until Captain Flinders, in 
his modest and enlightened paper on this subject, published 
in the Philosophical Transactions, suggested that they were 
probably owing to the concentration of the magnetic influence 
of the iron, made use of in the construction of the ship. The 
truth of this suggestion, and the accuracy of his observations, 
have since met with full confirmation, and his practical rules 
founded thereon have received additional support, from the 
“ Essay ” of Mr. Bain “ on the variation of the Compass,” 
published last year. 
As I have been materially anticipated by Mr. Bain, in a 
series of observations on the variation of the compass,* which 
* The azimuths contained in the following table were taken, either by the needle 
of a theodolite, or by a compass fitted up at sea, for the purpose, with a card made 
extremely light, and a bar fastened edgewise to it, by two brass screws, a a, as in 
the annexed sketch. The compass being small, the card light, and the needle very 
powerful, owing to the thickness of its ends, it performed considerably better than an 
expensive azimuth compass of larger dimensions, which indeed was so sluggish and 
erroneous in its indications, that I could make no good use of it. 
