At the centre of the island there is a chasm about fifty yards in diameter, whence the astronomers descend into a large dome, which is therefore called _flandona gagnole_, or the astronomer’s cave, situated at the depth of a hundred yards beneath the upper surface of the adamant. In this cave are twenty lamps continually burning, which, from the reflection of the adamant, cast a strong light into every part. The place is stored with great variety of sextants, quadrants, telescopes, astrolabes, and other astronomical instruments. But the greatest curiosity, upon which the fate of the island depends, is a loadstone of a prodigious size, in shape resembling a weaver’s shuttle. It is in length six yards, and in the thickest part at least three yards over. This magnet is sustained by a very strong axle of adamant passing through its middle, upon which it plays, and is poised so exactly that the weakest hand can turn it. It is hooped round with a hollow cylinder of adamant, four feet yards in diameter, placed horizontally, and supported by eight adamantine feet, each six yards high. In the middle of the concave side, there is a groove twelve inches deep, in which the extremities of the axle are lodged, and turned round as there is occasion.

The stone cannot be removed from its place by any force, because the hoop and its feet are one continued piece with that body of adamant which constitutes the bottom of the island.

By means of this loadstone, the island is made to rise and fall, and move from one place to another. For, with respect to that part of the earth over which the monarch presides, the stone is endued at one of its sides with an attractive power, and at the other with a repulsive. Upon placing the magnet erect, with its attracting end towards the earth, the island descends; but when the repelling extremity points downwards, the island mounts directly upwards. When the position of the stone is oblique, the motion of the island is so too: for in this magnet, the forces always act in lines parallel to its direction.

By this oblique motion, the island is conveyed to different parts of the monarch’s dominions. To explain the manner of its progress, let _A_ _B_ represent a line drawn across the dominions of Balnibarbi, let the line _c_ _d_ represent the loadstone, of which let _d_ be the repelling end, and _c_ the attracting end, the island being over _C_: let the stone be placed in position _c_ _d_, with its repelling end downwards; then the island will be driven upwards obliquely towards _D_. When it is arrived at _D_, let the stone be turned upon its axle, till its attracting end points towards _E_, and then the island will be carried obliquely towards _E_; where, if the stone be again turned upon its axle till it stands in the position _E_ _F_, with its repelling point downwards, the island will rise obliquely towards _F_, where, by directing the attracting end towards _G_, the island may be carried to _G_, and from _G_ to _H_, by turning the stone, so as to make its repelling extremity to point directly downward. And thus, by changing the situation of the stone, as often as there is occasion, the island is made to rise and fall by turns in an oblique direction, and by those alternate risings and fallings (the obliquity being not considerable) is conveyed from one part of the dominions to the other.