fills up the shores and empties them whilst it moves from a certain definite point in the sky back to the same point in a daily revolution. This motion of the waters is incited and the seas rise and fall no less when the moon is below the horizon and in the lowest part of the heavens, than if it had been raised at a height above the horizon. So the whole mass of the earth interposed[171] does not resist the action of the moon, when it is below the earth; but the seas bordering on our shores, in certain positions of the sky when it is below the horizon, are kept in motion, and likewise stirred by its power (though they are not struck by its rays nor illuminated by its light), rise, come up with great force, and recede. But about the reason of the tides anon[172]; here let it suffice to have merely touched the threshold of the question. In like manner nothing on the earth can be hidden from the magnetick disposition of the earth or of the stone, and all magnetical bodies are reduced to order by the dominant form of the earth, and loadstone and iron show sympathy with a loadstone though solid bodies be interposed. * * * * * CHAP. XVII. On the Iron Cap of a Loadstone, with which it is armed at the pole (for the sake of the _virtue) and on the efficacy of the same._ Conceive a small round plate, concave in shape, of the breadth of a digit to be applied to the convex polar surface of a loadstone and skilfully attached; or a piece of iron shaped like an acorn, rising from the base into an obtuse cone, hollowed out a little and fitted to the surface of the stone, to be tied to the loadstone. Let the iron be the best steel, smoothed, shining, and even. A loadstone with such an appliance, which before only bore four ounces of iron, will now raise twelve. But the greatest force of a combining or rather united nature is seen {87} when two loadstones, armed with iron caps, are so joined by their concurrent (commonly called contrary) ends, that they mutually * attract and raise one another. In this way a weight of twenty ounces is raised, when either stone unarmed would only allure four ounces of iron. Iron unites to an armed loadstone more firmly than to a loadstone; and on that account raises greater weights, because the pieces of iron stick more pertinaciously to one that is armed. For by the near presence of the magnet they are cemented together, and since the armature[173] conceives a magnetick vigour from its presence and the other conjoined piece of iron is at the same time endued with vigour from the presence of the loadstone, they are firmly bound together. Therefore by the mutual contact of strong pieces of iron, the cohesion is strong. Which thing is also made clear and is exhibited by means of rods sticking together, Bk. 3, chap 4[174]; and also when the question of the concretion of iron dust into a united body was discussed. For this reason a piece of iron set near a loadstone draws away any