It was arranged that Jack should take the first period, the professor the second, Mark the third and Washington the fourth. As the first watch had passed Jack was excused and the inventor said he would take charge of the ship. Then, as every one was tired from the happenings of the day, they all went to bed, excepting Amos Henderson, who entered the tower to steer the ship. The engines, dynamos and motors ran without much attention save such as the pilot might give them occasionally, for he could leave the ship with the steering wheel fastened, a few minutes at a time, as there was no danger of collisions. So the _Monarch_ continued to race toward the north. It was almost time for Mark's tour of duty to begin. The two boys, who were sleeping together, were in a deep slumber, when Washington ran in and shouted at the top of his voice: "Wake up everybody! De perfessor is killed dead!" Andy, Mark, Jack and the two helpers sat up in their bunks, rubbing their sleepy eyes and wondering what had happened. "What's the matter?" asked Jack. "Mr. Henderson is dead! He's in the engine room!" "What killed him?" inquired Andy. "He must hab got a shock from de dynamo!" Andy jumped from his bunk and hurried to the engine room. There, as the negro had described, Professor Henderson was lying white and senseless on the floor. The old hunter stooped over the inventor and felt of his heart. "He is alive!" he exclaimed. "His heart beats! We must carry him to a bunk!" Aided by Washington, Andy carried the professor to the sleeping room, where he was made comfortable in one of the beds. The captain was so near death that he could not be seen to breathe, and only the faint flutter of his heart told that life existed. "We're lost!" cried Washington. "If he dies we'll never get back home again. He is de only one dat knows how to mix de chemicals for de gas!" This was alarming news. Without the mysterious vapor the ship would not keep afloat long, nor could it be worked back from the desolate land of ice and snow. How much of the gas was left no one knew. "Did he ever get a shock like this before?" asked the hunter of Washington. "Once, but not so strong." "What did you do for him? What medicine did he take?" "Glory! Glory!" shouted the negro, jumping up and down in his excitement. "I remembers it now. Wait a second!" He hurried to the engine room, and came back in a little while with a small bottle. "Perfessor done say," he began, "dat if eber I seed him senselike, when he done gone and got a shock from de 'lectrisititeness, I was to gib him two spoons full ob dis." Andy took the bottle, which contained a red liquid. Bill got a spoon from the locker where the dishes were kept. With hands that trembled the old hunter poured out some of the fluid. Then, with Jack's help he forced open the inventor's mouth and put the medicine in. "I hope it works!" murmured Andy.