THE GREAT CUBE A cube of solid, polished steel, some twenty feet square, set on a spreading base of concrete, and divided perpendicularly down the middle into Titanic halves, these being snugly fitted one to the other by a series of triangular corrugations, a variation of the familiar tongue and groove.

Interlacing the ponderous mass, from corner to corner, were huge steel bolts, and the hulking heads of more bolts, some forty on each of the four sides, showed that the whole might be split into halves at will, and readily made whole again, one enormous side sliding back and forth on a short track.
In the two undivided faces of the cube, relatively squaring the center, were four borings somewhat smaller in diameter than an ordinary pencil, and extending through; and directly in the center was focused a network of insulated wires which dropped down out of the gloom overhead.

In the other two sides of the great cube, just where the dividing lines of the halves came, were the funnel-like mouths of a two-inch boring.

This, too, extended straight through.
Directly opposite each of the two mouths, a dozen feet away, was mounted a peculiarly-constructed heavy gun of the naval type.

In a general sort of way these were not unlike twelve-inch ordnance, but the breech was much larger in proportion, the barrel longer, and the bore only two instead of twelve inches.