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had its rise, and whence also the Principal Observations of the Change of its declination are come to us; so that 'tis just that the Observations, made elsewhere concerning the same, should return thither, as to its source.
I shall therefore let you know, that having alwayes been Curious in the Doctrine of the Load-stone, after I had made the Experiments that are in Gilbertus and others, I made that of the Needles Declination on three different Meridian-Lines, which I traced An. 1630. in several places of Paris, and found, that the Needle declined 4½ degrees North East: which having publisht, and made known here to the Curious and to Artists, some of whom counted 9 or 10 degrees according to the Tradition and Writings of Orontius Fineus, and Castelfranc; others, 11½ degrees, following Sennertus and Offusius: all at first rejected my Observation; and as commonly new things meet with obstacles and contradictions, before they are establisht, those that could not contradict what they saw, pretended, that this Variety did perhaps proceed from the greater or lesser vigour in the Loadstones, employed to touch with; or from thence, that the Needles had been touch't nearer to or farther from their Poles; which might make them decline more or less from the Meridian, so as a Needle, being precisely toucht by the Pole of a good Magnet, might perhaps have no Declination at all.
All which conjectures were not without their probability; which was the greater, in regard that all the Load-stones I had seen, being rude and like Flints, with irregular surfaces, in bunches and cavities, there Poles were always ill posited, and often within some of the Cavities, so that one could not be sure to strike the Needle thorow the Pole of the Stone. To remove which difficulty, and at the same to find another quality (one of the excellentest of the World, if true;) viz. that which Gilbert had assigned to Terrella's; I resolv'd to make the Experiment of it. And because I have not yet written of it, nor any man, I know, (Men having contented themselves with refuting this Error by Discourse only) you will perhaps not be displeased to be inform'd of the success thereof.
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