Shortly after this realization dawned, he was ordered below, and as the tropic sun was sinking over that eery floating tombstone, which according to Professor Stevens marked a nation's grave, the _Nereid_ submerged. Down she slid, a hundred fathoms or more, on a long, even glide that took her deep under that veiling brown blanket. * * * * * In the navigating room now, Larry stood with the captain, the professor and Diane, studying an illuminated panel on which appeared a cross of five squares, like a box opened out. The central square reproduced the scene below, while those to left and right depicted it from port and starboard, and those to front and rear revealed the forward and aft aspects of the panorama, thus affording a clear view in every direction. This, then, was the television device Professor Stevens had referred to the previous afternoon, its mechanical eyes enabling then to search every square inch of those mysterious depths, as they cruised along. It was the central square that occupied their attention chiefly, however, as they stood studying the panel. While the others represented merely an unbroken vista of greenish water, this one showed the sea floor as clearly as though they had been peering down into a shallow lagoon through a glass-bottomed boat, though it must have been a quarter of a mile below their cruising level. A wonderful and fearsome sight it was to Larry: like something seen in a nightmare--a fantastic desert waste of rocks and dunes, with here and there a yawning chasm whose ominous depths their ray failed to penetrate, and now and then a jutting plateau that would appear on the forward square and cause Captain Petersen to elevate their bow sharply. But more thrilling than this was their first glimpse of a sunken ship--a Spanish galleon, beyond a doubt! There she lay, grotesquely on her side, half rotted, half buried in the sand, but still discernible. And to Larry's wildly racing imagination, a flood of gold and jewels seemed to pour from her ruined coffers. * * * * * Turning to Diane, he saw that her eyes too were flashing with intense excitement. "Say!" he exclaimed. "Why don't we stop and look her over? There may be a fortune down there!" Professor Stevens promptly vetoed the suggestion, however. "I must remind you, young man," he said severely, "that this is not a treasure hunt." Whereupon Larry subsided; outwardly, at least. But when presently the central square revealed another and then another sunken ship, it was all he could do to contain himself. Now, suddenly, Diane cried out: "Oh, daddy, look! There's a modern ship! A--a freighter, isn't it?"