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the last year ** This Letter was written this present year. I found no more but 10 minutes on the same Meridian. Upon which having lately applied, since the receipt of the Letter, the same two Needles, me thinks, the Declination is yet less, than the last year. But this I can assure you, that the Declination is yet some minutes towards the East, at least at Paris. So that you may, upon my word, doubt ** By the favour of the Author, is not conclusive, that because the Declination is yet somewhat towards the East at Paris, that therefore it must be so at London: Since 'tis known here, that even the Variation of White-Hall differs from that of Lime-Houses which two places are but 4 English miles, or thereabouts, distant from one another. of the Observation of your friend, whom perhaps the Meridian, or the Needle, or the Construction and Division of his Compass may have deceived to a degree and a half North-east, which he at the present assigns to the Declination, But I doubt not, but in 12 or 15 years it will be found true what he affirms, as I have prognosticated by my Hypothesis, which maketh the Declination to vary a degree every seven or eight years.
This is, what I had to return to the Letter, which I wish might deserve to be presented to your Illustrious Society, and contribute something to the discovery of so many admirable vertues lodged in the Stone, and principally to the finding out of the Cause of this Variation; for which I have already made some attempt, and proposed my thoughts in a Dissiertation de Latitudine Parisiensi & Magnetis Declinatione, which M. du Hamel caused to be printed Anno 1660. with his Astronomia Physica, I shall be very glad, to learn the sentiment of your Learned Philosophers thereupon, and what cause they suspect there is of so singular an effect. I could discourse to you of other particulars touching the Proprieties of the Load stone, and especially of a remarkable one, I have discover'd, and which, if I am not deceived, subverts that Theory, which undertakes to explicate all these effects by the Pariculæ striatæ but I reserve that for another occasion.
