As to the South Poles, I take the _Asian_ Pole, which I place about the Meridian of the Island _Celebes_ to be the fixt, and consequently the _American_ Pole to move; from the like Observation of the slow Decrease of the Variation on the Coast of _Java_, and near the Meridian of the _Asian_ Pole; though I must confess to have no account of the effects of the other beyond _Magellan_'s Streights. If this be allow'd me, 'tis plain that the fixt Poles are the Poles of this External Shell or Cortex of the _Earth_, and the other two the Poles of a Magnetical _Nucleus_ included and moveable within the other. It likewise follows, that this Motion is Westwards, and by consequence that the aforesaid _Nucleus_ has not precisely attained the same degree of Velocity with the exteriour Parts in their diurnal Revolution; but so very nearly equals it, that in 365 Revolves the difference is scarce sensible. This I conceive to arise from the Impulse whereby this diurnal Motion was imprest on the Earth, being given to the External Parts, and from thence in time communicated to the Internal; but not so as perfectly to equal the Velocity of the first Motion impress'd on, and still conserv'd by the superficial Parts of the Globe. As to the quantity of this Motion it is almost impossible to define it, both from the Nature of this kind of Observation, which cannot be very accurately perform'd, as also from the small time these Variations have been observ'd, and their Change discover'd. It appears by all Circumstances, that its Period is of many Centuries of Years, and as far as may be collected from the Change of the Place, where there was no Variation, by reason of the Equilibre of the two Southern Magnetical Poles, _viz._ from _Cape d' Agulhas_ to the Meridian of St. _Helena_ (which is about 23 _degr._ in about ninety Years) and of the place where the Westerly Variation is in its ἀκμὴ or greatest Deflection, being about half so much, _viz._ from the Isle of _Diego Roiz_ to the South West Parts of _Madagascar_. We may with some Reason conjecture, that the _American_ Pole has mov'd Westwards forty six Degrees in that time, and that the whole Period thereof is perform'd in seven hundred Years, or thereabouts; so that the nice Determination of this, and of several other Particulars in the Magnetick System is reserv'd for remote Posterity; all that we can hope to do, is to leave behind us Observations that may be confided in, and to propose an Hypothesis which after Ages may examine, amend or refute. Only here I must take leave to recommend to all Masters of Ships, and all others, Lovers of Natural Truths, that they use their utmost Diligence to make, or procure to be made, Observations of these Variations in all parts of the World, as well in the North as South Latitude (after the laudable Custom of our _East India_ Commanders) and that they please to communicate them to the _Royal Society_, in order to leave as compleat a History as may be to