"How did it all happen?" asked Mr. Henderson, and Jack and Mark told what they knew of the explosion. "I was working over an extra air-pump that I wish to take along with us," stated Mr. Roumann, "when I was startled by seeing two strangers standing near my work bench. One I recognized as the insane machinist who was here before. The other--" "The other was the same one who looked in the window one night, and who, I believe, stole the power plates," interrupted Jack. "I wish I had known that," went on Mr. Roumann. "I would have made him give them back. But I did not have time to do anything. Before I could stop him the crazy machinist had thrown something at me, which I now know must have been a bomb. Then came the explosion, and knew nothing more until you revived me. Is the place much wrecked?" "I think not," answered Jack. "We will go look in a little while; just as soon as we see that you are all right," announced the professor. "Oh, I am all right. Go now. I am anxious to know." Having assured himself that the German was able to walk to the shop, Mr. Henderson an assent, and the two boys, Washington and two scientists started for the place where Annihilator was kept. "How did you happen to see it, Washington?" asked Mark. "I was out fixin' a loose board on mah chicken coop," explained the colored man, "when I seen dem two rapscallions come runnin' out ob de place. I knowed dey hadn't no right dere, an' I hollered at 'em. But dey didn't stop, an' de nextest t'ing I knowed dere was a big bang. I run in, an' I seed Mistah Roumann all blowed to pieces." "Hardly as bad as that," said the German with a smile. "Well, almost," insisted Washington. They reached the machine shop. The smoke had all cleared away, but the fumes from the bomb were still noticeable. "I wonder what their object could have been?" said Jack. "I believe they are urged on by some of my enemies," was the German's reply. "But let us see what damage has been done. I hope it is not much." Pieces of broken machinery, twisted wheels, bent levers, shattered cogs and smashed plates were all about one corner of the shop. But the great projectile was still in place. It had not even been jarred. Mr. Roumann went to an opening in the side that led to the engine-room. No sooner had he entered than he uttered a cry. "The Etherium motor is damaged!" he exclaimed, and with fear in their hearts the others followed him inside the Annihilator. CHAPTER XIII AN ALARMING THREAT The main machines in the engine-room were the two motors, one designed to send the projectile through the atmosphere, the other intended to propel it through the space filled with what is called ether. It was to these two massive machines that the eyes of all were now directed. The smaller one, the atmospheric motor, did not appear to have been damaged, but several wheels and pipes of the other were broken and twisted. "Is it ruined?" asked Professor Henderson.