such a way that its austral pole may be toward the boreal pole of the one that is swimming, and near it, sideways: for the floating stone forthwith follows the other stone (provided it be within its force and dominion) and does not leave off nor forsake it until it adhæres; unless by withdrawing your hand, you cautiously avoid contact. In like manner if you set the boreal pole of the one you hold in your hand opposite the austral pole of the swimming stone, they rush together and follow each other in turn. For contrary poles allure contrary. If, however, you apply in the same way the northern to the northern, and the austral to the austral pole, the one stone puts the other to flight, and it turns aside as though a pilot were pulling at the helm and it makes sail in the opposite ward as one that ploughs the sea, and neither stands anywhere, nor halts, if the other is in pursuit. For stone disposeth stone; the one turns the other around, reduces it to range, and brings it back to harmony with itself. When, however, they come together and are conjoined according to the order of nature, they cohære firmly mutually. For instance, if you were to set the boreal pole of that stone which is in your hand before the tropic of Capricorn of a round floating loadstone (for it will be well to mark out on the round stone, that is the terrella, the mathematical circles as we do on a globe itself), or before any point between the æquator and the austral pole; at once the swimming stone revolves, and so arranges itself that its austral pole touches the other's boreal pole, and forms a close union with it. In the same way, again, at the other side of the æquator, with the opposite poles, you may produce similar results; and thus by this art and subtilty we exhibit attraction, repulsion, and circular motion for attaining a position of agreement and for declining hostile encounters. Moreover 'tis in one and the same stone that we are thus able to demonstrate all these things and also how the same part of one stone may on division become either boreal or austral. Let A D be an oblong stone, in which A is the northern, D the southern pole; cut this into two equal parts, then set part A in its vessel on the water, so as to float.
And
