“I believe you’ve struck it,” said Professor Palmer. “And I believe the big ‘checker-board’ is nothing more nor less than a device for absorbing power from the sun’s rays. That alone would explain the Martians’ remarkable achievements in the face of the unquestionable dwindling, perhaps complete exhaustion, of the planet’s fuel supply.” “How old do you suppose Mars is!” asked Robert. “That’s a hard one; but the various planets are classified according to stages. There is the sun stage, in which the planet is hot enough to emit light. This is followed by the molten stage--hot, but lightless. Then comes the solidifying stage, with the formation of solid surfaces and ocean basins. The next stage is what we call the terraqueous stage, the age of sedimentary rocks. Our Earth is in this stage. Following this is the terrestrial stage, in which the oceans have disappeared, and, after that the dead stage, when air has departed. Mars is in the terrestrial stage, the stage following that of our planet, and preceding the dead, or final stage.” “Then the Martians are engaged in a constant struggle against extinction!” “They are, though, with their marvelous ingenuity, they may last a few thousand years longer. But we are witnesses of the waning of a world.” They were now passing through a fertile farming region. Small buildings dotted the landscape, while here and there Martian farmers were diligently at work in their fields. There was a complete absence, however, of any beast of burden or toil. Everywhere power seemed to be furnished electrically. Farmers could be seen plowing with large, powerful tractors. Frequently they caught glimpses of the checker-board devices adjoining the buildings, but on a much smaller scale than the one they had first seen. Quite likely, they decided, these were individual sun-power plants. With the increasing frequency of houses, Robert and the professor became convinced that they were nearing a center of population. Their interest was keyed to the highest pitch as the agricultural district gave way to the outskirts of a Martian city. The more Robert saw, the greater was his surprize at the striking similarity of things to those on Earth. Yet, on second thought, this did not seem so strange. After all, it was to be expected that the chief inventions of two such advanced worlds should, in the main, be similar. He might easily have imagined himself approaching some foreign metropolis. One thing that they noticed particularly was the absence of the dirt and squalor which one so frequently sees from the train when approaching our large industrial centers. Buildings all seemed of substantial construction and everywhere were in excellent condition.