The Amtorians have developed a compass similar to ours. According to Kiron, it points always toward the center of Amtor—that is, toward the center of the mythical circular area called Strabol, or Hot Country. This statement assured me that I was in the southern hemisphere of the planet, the needle of the compass, of course, pointing north toward the north magnetic pole. Having no sun, moon, nor stars, their navigation is all done by dead reckoning; but they have developed instruments of extreme delicacy that locate land at great distances, accurately indicating this distance and the direction; others that determine speed, mileage, and drift, as well as a depth gauge wherewith they may record soundings anywhere within a radius of a mile from the ship. All of their instruments for measuring distances utilize the radio-activity of the nuclei of various elements to accomplish their ends. The gamma ray, for which they have, of course, another name, being uninfluenced by the most powerful magnetic forces, is naturally the ideal medium for their purposes. It moves in a straight line and at uniform speed until it meets an obstruction, where, even though it may not be deflected, it is retarded, the instrument recording such retardation and the distance at which it occurs. The sounding device utilizes the same principle. The instrument records the distance from the ship at which the ray encounters the resistance of the ocean’s bottom; by constructing a right triangle with this distance representing the hypotenuse it is simple to compute both the depth of the ocean and the distance from the ship at which bottom was found, for they have a triangle of which one side and all three angles are known. Owing to their extremely faulty maps, however, the value of these instruments has been greatly reduced, for no matter what course they lay, other than due north, if they move in a straight line they are always approaching the antarctic regions. They may know that land is ahead and its distance, but they are never sure what land it is, except where the journey is a short and familiar one. For this reason they cruise within sight of land wherever that is practical, with the result that journeys that might otherwise be short are greatly protracted. Another result is that the radius of Amtorian maritime exploration has been greatly circumscribed; so much so that I believe there are enormous areas in the south temperate zone that have never been discovered by the Vepajans or the Thorists, while the very existence of the northern hemisphere is even unguessed by them. On the maps that Danus showed me considerable areas contained nothing but the single word _joram_, ocean. However, notwithstanding all this (and possibly because of it), I was confident that we could manage to navigate the ship quite as satisfactorily as her present officers, and in this Kiron agreed.