"Back, everyone!" roared Dr. Bird.
he men sprang back. The searing ray approached the bar. It touched it, and bar and truck disappeared into thin air. A splutter of sparks came from the severed ends of the wire. The ray disappeared. Carnes rubbed his eyes. Where the truck had rested on solid ground was now a gaping wound in the earth.
"Projector forward!" cried the doctor. "Hurry, men!"
The trucks bearing the battery of projectors moved forward until they were at the edge of the hole. Portable cranes swung the lamps out, and men swarmed over them. The projectors were pointed down the hole. Carnes joined the doctor in peering down. A hundred yards below them the terrible ray was blazing. As they watched, its end came in sight. The ray was being projected forward from the end of a black cigar-shaped machine which was slowly moving forward.
"That's your target, men!" cried the doctor. "Align on it and signal when you are ready!"
One by one the projector operators raised their hands in the signal of "ready." Still the doctor waited. Suddenly the forward movement of the black body ceased. The ray was stationary for a moment and then moved slowly upward. A terrific roaring came from the cavern.
"Projector switch!" roared the doctor, his heavy voice sounding over the tumult.
"Ready, sir!" a shrill voice answered.