“I must, beloved,” he replied, tenderly. “They still depend upon me to operate the _Sphere_ safely in an emergency. I can not refuse the professor this service. Why, if it hadn’t been for him, I could not have come to Mars, and you would still have been the emperor’s prisoner.” “You are right. I’m afraid I am just a selfish girl with foolish fears. You must hurry now and come back to me quickly, dear.” So they parted, Robert promising to come back to her as soon as possible, each striving to conquer a nameless fear that they would never see each other again. A few hours later found the _Sphere_ approaching the pole at a tremendous speed. Accompanying Robert and his companions were three Martian experts. Two of these were astronomers; the other, a professor of physics, acted as their guide. Far away to the north a comparatively small expanse of white indicated what remained of the great polar cap of ice and snow that, during the winter, extended over the entire region. “How is the water from the melting snows accumulated for distribution?” Taggert asked. “As the spring advances, and the edges of the vast polar cap of snow begin to melt, the water is collected in the sea basins,” explained the professor of physics. “But the task of running the great ducts beneath the shores of these seas in order to connect with and drain their lowest points seems almost an impossible one.” “Quite true. That plan was finally rejected for that very reason. A system of siphons was built instead. Even this must have been a tremendous task--our history records that it required more than a century to complete it; yet so remarkable was this construction that the original work, now many centuries old, still remains in perfect condition.” * * * * * Robert dropped the _Sphere_ to within a half mile of the surface. They were passing over what appeared to be a great basin of some sea. Continuing northward they passed beyond the first great basin and over several smaller ones. The white polar cap was less than thirty miles away. As they neared it a small expanse of water in the lowest depressions of the basin became visible. “Ah, that must be one of the siphons!” exclaimed Professor Palmer, pointing. A small, sinuous ridge ran from the south along the bottom of the basin, disappearing in the little patch of water. “Yes, that is one of them,” confirmed their guide. “No doubt it is perplexing to you as to how each canal is supplied with water without interruption as the water in the seas and the polar cap is consumed and recedes.” “That is true,” admitted Professor Palmer.