A murmur of assent answered him and the line formed and started across the swamp. They had gone perhaps a hundred yards when three red lights came from one of the planes circling overhead.
"Down!" cried the doctor, dropping to his knees in the muck.
Four hundred yards ahead of them a concrete platform emerged from the marsh and rose slowly into the air. It was roofed with a dome of what looked like plate glass, but which the doctor shrewdly suspected was vitrilene. When the base of the platform was two-feet above the level of the water the dome slid silently aside disclosing two men bending over a tiny gun. Dr. Bird leveled his binoculars.
"That's the Breslau gun model that was stolen as sure as I'm a foot high!" he cried. "They must have made some miniature shells and be planning to fire it."
Slowly a pall of intense blackness rose from the marsh and enveloped the platform and hid it from view. A whining noise came from overhead, and then a crash like a thunderbolt. The blast of the explosion threw the attackers face down in the swamp, and when they arose and looked back there was merely a gaping hole where the leading tank had been. The second tank suddenly seemed to rise in the air and fly into millions of tiny fragments, and a second thunderous blast sent them again to their knees.
"Radite!" bellowed Dr. Bird to Carnes. "Imagine the effect if that had been a full charge fired from a completed Breslau gun! Watch the planes, now. I think they are going to drop a few eggs on them."
he black mist cleared as if by magic and the platform was in plain view. The big glass dome rolled back into place as the two planes swept over at an elevation of two thousand feet. From each one a small black cigar-shaped object was released and fell in a long parabola toward the earth. The glass dome which had been closing over the gun platform rolled quickly back and a long beam of intense blackness pierced the heavens. First one and then the other of the falling bombs disappeared from view into it, and then the black column faded from view. The two bombs fell with increasing speed but the dome closed over the platform before they struck. The two hit the dome at almost the same instant and instead of the blinding crash they expected, the watchers saw the bombs rebound from the dome and fall harmlessly into the water.
"Stymied!" muttered the doctor. "I wonder what other properties that confounded lamp has."