Resort to this method of guidance soon was a necessity. It proved to be not so simple as expected; for, as the flakes fell faster and faster, the great cakes of ice were not visible until they were almost upon them, and then they had an awkward habit of appearing only after the adventurers had fallen over them. Stumbling along, with Professor Palmer keeping pace with difficulty beside him, Robert felt that surely they must have passed the _Sphere_ already. It seemed to him that they had walked two miles or more since they had turned back, and still the _Sphere_ could not be seen. He turned an instant and looked back half expecting to catch a glimpse of it behind. Taggert trudged along a few feet back; the others were strung out two or three yards in the rear. A minute later Robert heard a muffled cry behind him. He turned just in time to see Taggert fall and slip from view in the blinding snow. Robert took a quick step to the reporter’s aid. The next instant his feet shot from under him and he tobogganed down the slippery incline of ice toward the sea. One thought reassured him as he felt the smooth surface racing past him: the level, unbroken expanse of ice over the sea would surely stop him when he reached it. But, hard on the heels of this thought, came the realization that, with all sense of direction lost out on the expanse of ice in a blinding snow, he might blunder farther and farther away from the _Sphere_. He earnestly hoped that the end of his slide would at least bring him close to Taggert. Presently he reached the bottom of the incline and shot out over the smooth, frozen surface of the sea. Here his momentum was quickly checked. As soon as he could regain his feet he stood up and peered round him. But only the driving snow, which all but obscured his hand before him, rewarded his gaze. He shouted several times, listening intently after each call. The snow seemed to muffle his cries in the making. Nothing was visible round him but a mil of snowflakes. His ears tingled with the bitter cold even under the fur cap he wore. He shouted again, removing his cap to listen afterward. A faint answering cry floated back to him; but whether this was simply the rebound of his own cry from the dense wall of snow he did not know. As he continued to listen the same faint cry again came to him, this time a bit stronger, seemingly from away to his left. He clapped his cap on and strode off in that direction. Several times he called out again, stopping to listen each time. Again that faint echo mocked him, but this time it seemed to come from behind. The well-known difficulty of determining the direction from which a sound comes in a fog came to Robert’s mind, and he despaired as he realized the same difficulty in attempting to find a distant call in the falling snow.