Hastening away to the mine, he had the chamber where the powder was to be lodged enlarged the whole breadth and height of the sloping rock against which the wall leaned, till the upper part was about a foot thick, and had to be propped up to prevent its falling in. A strong stake was fixed firmly on the granite foundation, on the top of which the dead fox was fastened. A rope was attached to the lower part of the stake, sufficiently long to reach the powder stores. "This is the bait," he said, pointing to the dead fox, "and here is the mine," he added, rolling in a keg of powder containing about 100 lbs. "But, Doctor," said Hatteras, "won't that blow us up too, as well as the bears?" "No, we shall be too far from the scene of explosion. Besides, our house is solid, and we can soon repair the walls even if they should get a bit shaken." "And how do you propose to manage?" asked Altamont. "See! By hauling in this rope we lower the post which props up the roof, and make it give way, and bring up the dead fox to light, and I think you will agree with me that the bears are so famished with their long fasting, that they won't lose much time in rushing towards their unexpected meal. Well, just at that very moment, I shall set fire to the mine, and blow up both the guests and the meal." "Capital! Capital!" shouted Johnson, who had been listening with intense interest. [Illustration: ] Hatteras said nothing, for he had such absolute confidence in his friend that he wanted no further explanation. But Altamont must know the why and wherefore of everything. "But Doctor," he said, "can you reckon on your match so exactly that you can be quite sure it will fire the mine at the right moment?" "I don't need to reckon at all; that's a difficulty easily got over." "Then you have a match a hundred feet long?" "No." "You are simply going to lay a train of powder." "No, that might miss fire." "Well, there is no way then but for one of us to devote his life to the others, and go and light the powder himself." "I'm ready," said Johnson, eagerly, "ready and willing." "Quite useless my brave fellow," replied the Doctor, holding out his hand. "All our lives are precious, and they will be all spared, thank God!" "Well, I give it up!" said the American. "I'll make no more guesses." "I should like to know what is the good of learning physics," said the Doctor, smiling, "if they can't help a man at a pinch like this. Haven't we an electric battery, and long enough lines attached to it to serve our purpose? We can fire our mine whenever we please in an instant, and without the slightest danger." "Hurrah!" exclaimed Johnson. "Hurrah!" echoed the others, without heeding whether the enemy heard them or not. The Doctor's idea was immediately carried out, and the connecting lines uncoiled and laid down from the house to the chamber of the mine, one end of each remaining attached to the electric pile, and the other inserted into the keg of powder.