_A._ I have one question more to ask concerning gravity. If gravity be, as some define it, an intrinsical quality, whereby a body descendeth towards the centre of the earth, how is it possible that a piece of iron that hath this intrinsical quality should rise from the earth, to go to a loadstone? Hath it also an intrinsical quality to go from the earth? It cannot be. The cause therefore must be extrinsical. And because when they are come together in the air, if you leave them to their own nature, they will fall down together, they must also have some like extrinsical cause. And so this magnetic virtue will be such another virtue as makes all heavy bodies to descend, in this our world, to the earth. If therefore you can from this your hypothesis of compounded motion, by which you have so probably salved the problem of gravity, salve also this of the loadstone, I shall acknowledge both your hypothesis to be true, and your conclusion to be well deduced. _B._ I think it not impossible. But I will proceed no farther in it now, than, for the facilitating of the demonstrations, to tell you the several proprieties of the magnet, whereof I am to show the causes. As first, that iron, and no other body, at some little distance, though heavy, will rise to it. Secondly, that if it be laid upon a still water in a floating vessel, and left to itself, it will turn itself till it lie in a meridian, that is to say, with one and the same line still north and south. Thirdly, if you take a long slender piece of iron, and apply the loadstone to it, and, according to the position of the poles of the loadstone, draw it over to the end of the iron, the iron will have the same poles with the magnet, so it be drawn with some pressure; but the poles will lie in a contrary position; and also this long iron will draw other iron to it as the magnet doth. Fourthly, this long iron, if it be so small as that poised upon a pin, the weight of it have no visible effect, the navigators use it for the needle of their compass, because it points north and south; saving that in most places by particular accidents it is diverted; which diversion is called the variation of the horizontal needle. Fifthly, the same needle placed in a plane perpendicular to the horizon, hath another motion called the inclination. Which that you may the better conceive, draw a fourth figure; wherein let there be a circle to represent the terrella, that is to say, a spherical magnet. _A._ Let this be it, whose centre is A, the north pole B, the south pole C. _B._ Join B C, and cross it at right angles with the diameter D E. _A._ It is done. _B._ Upon the point D set the needle parallel to B C, with the cross of the south pole, and the barb for the north; and describe a square about the circle B D C E, and divide the arch D B into four equal parts in _a_, _b_, _c._ _A._ It is done.