Sam built up the fire with generous hand. Its light as well as warmth was welcome, for the early dusk was closing in. The boys ranged themselves before the hearth. Coats were stripped off; shoes were removed, and toes were toasted comfortably. After all, the adventurers could count themselves lucky. If they had doubts on the point, they had but to listen to the shriek of the wind and the crackling sound of the snow driving against the windows. There was little talk. Now and then one or two of the party uneasily shifted position, but the others seemed to be content to sit quietly, gazing thoughtfully at the fire. The Shark especially was absorbed in reflections. Step, his right hand neighbor and one of the more nervous of the brotherhood, wriggled his long legs, stretched his arms, turned, and peered at the impassive Shark. “Oh, I say!” he broke out impatiently. “What’s the use of being a graven image? Come to life, Shark!” Very deliberately the youth addressed gave his attention to Step. “Huh! I’m very much alive,” he remarked calmly. “I’m doing something with such brains as I happen to have.” “How? What?” “I’m thinking.” “How we’ll get out of this fix?” The Shark frowned. “That would be wasted effort. There’s nothing we can do till the storm ends. Meanwhile, I entertain myself sensibly.” “But how?” Step insisted curiously. An instant the Shark hesitated. “I--I don’t know that you’d be interested.” “Hang it! I’d be interested in anything.” “Very well, then,” said the Shark. “Visualize a cube!” Up went Step’s hands. “Don’t shoot! I’ll come down. Also I’ll bite.” “What do you mean?” “It’s a catch, isn’t it? Go ahead! Spring your joke!” The Shark looked disgusted. “Joke nothing! See here, Step! You know what a cube is, don’t you? Well, visualizing one means just picturing it in your mind. Remember the formula, don’t you, for A + B, cubed? It’s A cubed + 3A squared, B + 3AB squared + B cubed. Now, take numbers instead of letters--take easy numbers. Call A + B fifteen.” “Er--er--all right. It’s fifteen. I don’t object.” “Likewise, we’ll call A ten and B five. Therefore the block representing the cube of A + B will be made up of a cube of A--say, we’ll call the units inches----” “I’m willing.” “Then the cube of A,” the Shark went on, “will be a rectangular block, ten inches in each direction. On three of its faces we place what I may term flat blocks, each ten inches square and five inches thick--they’re the A squared B fellows. Then come what we’ll describe as the long blocks, five inches two ways and ten inches the other. Finally, there’s the cube of B, a block five inches high, five inches wide, five inches thick. Putting these together, and picturing each clearly in mind----” Step’s long arm shot out. His hand fell on the Shark’s shoulder. “You villain! You traitor! Doing stunts like that--in vacation! You ought to be----”