"I should say not! If they use it, we've got 'em. That stuff has weight and the minute this beam of ours hits it, it will intensify the effect, and no matter how much pressure they have on it, it will blow up all over the place.... All set? Let's go. Throw in your switch, Murray." Murray did as directed. There was a humming sound and the tiny beam of light leaped across the rear end of the ship and out the exhaust. Across it fell a thin powder of iron filings--the material that was to be decomposed to furnish the power. Bang! With a roar, the _Monitor_ leaped forward, throwing all of them back into their heavily padded seats, then dipped and soared as the wings came into play. The passengers glanced through the windows. Beneath them the outskirts of Philadelphia were already speeding by. "Say," said Ben, "this is some bus. We must be making five hundred miles an hour." "Sure," said Sherman. "We could do over seven hundred as a pure projectile, but we can't use that much speed and keep our maneuvering power." CHAPTER XX The Coming of the Green Globes "Where to, folks?" asked Sherman, during one of their periods of soaring, as they floated high above the hilly country to the west of the Delaware River. "Oh, most anywhere," said Ben. "I would like to see you try out this new-fangled gun of yours on something, though." "What shall we try it on? A house?" "No, that's too easy. We saw what it could do to things like that in the laboratory. Find a nice rock." "O. K. Here goes. Don't give her the gun for a minute, Murray." With wings extended, the _Monitor_ spiralled down toward the crest of the mountain. A projecting cliff stood just beneath them, sharply outlined in the rays of the morning sun. "Now this is going to be difficult," warned Sherman. "Throw that connecting bar, Ben. It holds the power switch and the beam switch together so they're both turned on at once. Otherwise the recoil we'd get on this end of the beam would tumble us over backward. Hold it, while I set the controls. We've got to take a jump as soon as we fire, or we'll pop right into the mess we make.... Ready? All right, Gloria, go ahead with your searchlight." The beam of the searchlight shot out, pale in the daylight, wavered a second, then outlined the crest of the cliff. "Shoot!" cried Sherman. There was a terrific report; a shock; the _Monitor_ leaped, quivering in every part, and as they spiralled down to see what damage they had done, they beheld no cliff at all, but a rounded cup at the tip of the mountain in which a mass of molten rock boiled and simmered. "Fair enough," said Ben. "I guess that will do for the Lassans, all right. Home, James?" "Right," answered Sherman. "We've found out all we want to know this trip."