But there was another trouble of a different nature. The absence of sun and stars deprived them of the ordinary means of discovering their place. They could only make a rough guess as to the direction in which they were going. The gyrostatic compasses gave them considerable assistance, and they had perfect chronometers, but these latter could be of no use without celestial observations of some kind. At length Cosmo devised a means of obtaining observations that were of sufficient value to partially serve their purpose. He found that while the disk of the sun was completely hidden in the watery sky, yet it was possible to determine its location by means of the varying intensity of the light. Where the sun was a concentrated glow appeared, shading gradually off on all sides. With infinite pains Cosmo, assisted by the experience of the captain, succeeded in determining the center of the maximum illumination, and, assuming that to represent the true place of the sun, they got something in the nature of observations for altitude and azimuth, and Captain Arms even drew on his chart "Sumner lines" to determine the position of the Ark, although he smiled at the thought of their absurd inaccuracy. Still, it was the best they could do, and was better than nothing at all. They kept a log going also, although, as the captain pointed out, it was not of much use to know how fast they were traveling, since they could not know the precise direction, within a whole point of the compass, or perhaps several points. "Besides," he remarked, "what do we know of the currents? This is not the old Atlantic. If I could feel the Gulf Stream I'd know whereabouts I was, but these currents come from all directions, and a man might as well try to navigate in a tub of boiling water." "But we can, at least, keep working eastward," said Cosmo. "My idea is first to make enough southing to get into the latitude of the Sahara Desert, and then run directly east, so as to cross Africa where there are no mountains, and where we shall be certain of having plenty of water under our keel. "Then, having got somewhere in the neighborhood of Suez, we can steer down into the region of the Indian Ocean, and circle round south of the Himalayas. I want to keep an eye on those mountains, and stay around the place where they disappear, because that will be the first part of the earth to emerge from the flood and it is there that we shall ultimately make land." "Well, we're averaging eight knots," said the captain, "and at that rate we ought to be in the longitude of the African coast in about twenty days. How high will the water stand then?"