But though they spent much time taking photographs of the planets and of the moon, and in making spectrum analyses of the sun, time passed very slowly. Day after day they saw measured on the clocks, but they stayed awake, finding they needed little sleep, for they wasted no physical energy. Their weightlessness eliminated fatigue. However, they determined that during the twelve hours before reaching Venus they must be thoroughly alert, so they tried to sleep in pairs. Arcot and Morey were the first to seek slumber--but Morpheus seemed to be a mundane god, for he did not reward them. At last it became necessary for them to take a mild opiate, for their muscles refused to permit their tired brains to sleep. It was twelve hours later when they awoke, to relieve Wade and Fuller. They spent most of the twelve hours of their routine watch in playing games of chess. There was little to be done. The silver globe before them seemed unchanging, for they were still so far away it seemed little larger than the moon does when seen from Earth. But at last it was time for the effects of the mild drug to wear off, and for Wade and Fuller to awaken from their sleep. "Morey--I've an idea!" There was an expression of perfect innocence on Arcot's face--but a twinkle of humor in his eyes. "I wonder if it might not be interesting to observe the reactions of a man waking suddenly from sleep to find himself alone in space?" He stared thoughtfully at the control that would make the ship perfectly transparent, perfectly invisible. "I wonder if it would?" said Morey grasping Arcot's idea. "What do you say we try it?" Arcot turned the little switch--and where there had been the ship, it was no more--it was gone! Fuller stirred uneasily in his bed, tightly strapped as he was. The effects of the drug were wearing off. Sleepily he yawned--stretched, and blindly, his heavy eyes still closed, released the straps that held him in bed. Yawning widely he opened his eyes--with a sudden start sat upright--then, with an excellent imitation of an Indian on the warpath, he leaped from his bed, and started to run wildly across the floor. His eyes were raised to the place where the ceiling should have been--he called lustily in alarm--then suddenly he was flying up--and crashed heavily against the invisible ceiling! His face was a picture of utter astonishment as he fell lightly to the floor--then slowly it changed, and took on a chagrined smile--he understood! He spun around as loud cries suddenly resounded from Wade's room across the hall--then there was a dull thud, as he too, forgetting the weightlessness, jumped and hit the ceiling. Then the cries were gone, like the snuffing of a candle. From the control room there rose loud laughter--and a moment later they felt more normal, as they again saw the four strong walls about them. Wade sighed heavily and shook his head.