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Sir, As any improvement, or discovery in the arts and sciences, will, I am persuaded, experience your favourable reception, I have the honour of submitting to your consideration a dis­covery I have made on a subject, the state of which can only be ascertained by observations made from time to time, as it is not regulated by any known law of nature: I mean the variation of the magnetical needle. This discovery may not only excite others to make, and repeat, observations in different parts of the globe, but, by causing this changeable quality to be better understood, may contribute to the benefit of navigation, and commerce, as well as to the advancement of a more particular knowledge of the subject.

philosophical transactions of the royal society of london

XVIII. Observations on the permanency of the variation of the compass at Jamaica. In a letter from Mr. James Robertson to the Right Hon, Sir Joseph Banks, K. B. P. R. S. &amp;c