little crane swung the first metal work into position above the shaft. One end of the assembled framework of aluminum alloy dragged loosely on the ground; the other end swung out and projected above the shaft, swayed for an instant—and then came the first direct knowledge of the enemy's presence. The end of a metal strut, though nothing visible was touching it, grew suddenly white hot, sagged, then broke into a shower of molten, dazzling drops that rained down into the pit.
"Good," said Colonel Culver, who was standing beside Smithy. "Now we know they are there—but it means we will have to go down there with our gas masks on."
To Smithy it was not immediately apparent how gas masks were to protect them from the deadly invisible ray. He got the connection of thoughts when a bomb was slid over the edge. The dull thud of the explosion quickly came back to them.
"They popped that one off in the air—hit it with their heat ray," said a cheerful voice beside them. "But the phosgene will keep on going down. Give them another!"
The interval this time was longer. "Now for a dirty crack," said the cheerful voice. "Time this one."
youngster nearby snapped a stop-watch as the bomb was released. He held some printed tables in his hands. Odd receivers from which no wire led were clamped over his ears. This time the dull thud was long in coming. It was hardly perceptible when the young man with the stop watch announced: "Fifty thousand feet, sir."
"Give 'em another. Time it again." A second high explosive bomb was released.