"Great God!" gasped Davis. "Now where's Varrhus?"
The heavy masks the two aviators had worn had protected them from the flaming hydrogen, and their goggles had saved their eyes. Now Davis was only eager to make a second attempt upon the black machine. He swerved and circled. The searchlights below were waving frantically through the air. The flare aloft had been seen, and they concentrated upon the space below the spot. In a second the black flyer was once more outlined by half a dozen beams. Davis banked sharply and darted toward it again.
The pilot of the strange machine seemed to be quite confident that he had disposed of his antagonist, and was apparently busy with something inside the cabin. He was probably preparing to release his cold bomb, but was again interrupted. The biplane approached. Teddy saw his explosive bullets strike and flash. He knew they struck, but they seemed incapable of doing harm. The black flyer was clearly defined by the searchlights, and Teddy could see it distinctly. It was a long, needlelike body with a glass-inclosed cabin near the center. Above it four whirring disks of comparatively huge size showed the position of the vertical propellers that enabled it to rise and fall and to hang suspended motionless in the air. A fifth propeller spun slowly at the bow. That was evidently not running at full speed. Below the needlelike body hung a misshapen globe, like the bulging ovipositor of some strange insect.
Flash! Flash! The impact of the explosive bullets was marked by spiteful cracks as they burst. Teddy was aiming for the cabin of the machine.
"Got him!" he exclaimed.
The glass of the cabin windows had splintered into fragments. The aëroplane shot toward the motionless black flyer.
"Shall I ram?" asked Davis in a perfectly even voice. He was quite prepared to sacrifice both his and Teddy's lives to make absolutely certain of the destruction of the menacing helicopter with its more than dangerous occupant.
Teddy, with lips compressed, nodded. He had forgotten that in the darkness Davis could not see his movement. As the biplane sped forward the black machine dropped again. Again the whitish cloud was left behind it, clearly defined in the searchlight rays. Teddy had barely time to press the flare button before they reached the cloud. The mist of atomized liquid hydrogen seemed to burst into flame all about them. The aëroplane roared through hell-fire for a moment. Flame was before Teddy's aviator's goggles. He was in a veritable inferno. Then the aëroplane shot free again.
"Ram him!" panted Teddy. "Smash him! Do anything, only we've got to get him!"
They circled swiftly, searching for the black flyer. The searchlights were following him now, and they saw that he was rising straight up. He had not yet dropped his cold bomb. Davis put his machine at the ascent at as steep an angle as he dared. They climbed almost as rapidly as the helicopter. The black machine made its first aggressive move now. Davis was climbing in a jerky spiral, rising at an amazing speed. Teddy was busily fitting a new belt of cartridges into his machine gun. The pilot of the other machine darted to one side and a huge cloud of mist sprang into being just below him, darting downward like some pale-gray snake, unfolding itself in the sky. Davis zoomed sharply. Another second and he would have run into the whitish cloud. The biplane recovered and swerved to one side. Twelve thousand feet. Thirteen thousand feet. Fourteen thousand feet. Three miles in the air! Then the black flyer began to drop. The biplane dived after him, Teddy's machine-gun spitting fire and explosive bullets in a furious, well-directed blast. Once, twice, bursts of the little flashes that showed his bullets were striking served to reassure Teddy, but the biplane could not gain on the falling helicopter.
Down, down——There were half a dozen quick bursts of flame in the air. Anti-aircraft guns were firing. The black flyer dropped unharmed. Barely a thousand feet above the waters of the bay, the propeller at the bow seemed to be put into motion, for the straight descent changed into a graceful curve. The curve flattened out, and the black machine ceased to fall. It sped madly for the Narrows, with a bedlam of bursting shells all about it and the vengeful, spitting two-seater darting after it like an avenging Nemesis. Again and again spurts of flame against the body of the glistening helicopter showed that Teddy's fire was well directed, but the machine shot onward in a furious rush for the Narrows. Above the Narrows, without pausing, a black object that turned to white in the searchlight rays fell from the misshapen globe below the center of the black flyer's body. The thing that fell seemed to leave a mist of fog behind it as it dropped. Then, its mission accomplished, the dark machine fled toward the west.
Teddy and Davis, in the biplane, sped after it at the topmost speed of which their aëroplane was capable. Teddy was nearly insane with baffled rage and disappointment. He knew that he had failed. Another cold bomb had been dropped in the Narrows, and any attempt to destroy it would only result in the death of those who made the attempt.
"Faster, faster!" he pleaded to Davis. "If it gets far ahead of us we'll lose it in the darkness."
Davis pressed his lips together and used every artifice he knew of to increase the speed of his machine, but the glistening black body ahead of them drew steadily farther away. At last it could barely be seen. Then, as if in derision, a light appeared in the cabin of the black flyer. It winked oddly. Dot-dash, dot-dash——
"He's signaling," said Davis.
Dot-dash, dot-dash——
"W-a-t-c-h," spelled Davis, "t-h-e M-i-s-s-i-s-s-i-p-p-i.—V-a-r-r-h-u-s."
"Watch the Mississippi, Varrhus," repeated Teddy. "He's getting away! He's getting away!"
The light ahead of them winked and disappeared. The sky was empty except for the biplane roaring after a vanished enemy.
"He's gotten away," half sobbed Davis. "Damn him! He killed Curtiss, and he's gotten away!"
Teddy stared into the empty night with something of Davis' disappointment and despair.
CHAPTER IX.
Next morning the world read at its breakfast table that the Mississippi River had frozen over just below St. Louis, and that the water was rising rapidly. The river had frozen solidly up to the surface. The level rose, and the water started to flow over the top of the ice cake, only to be turned into ice as it did so. Hour by hour the level rose, and hour by hour the solid ice barrier rose with the water level. Men had tried to blast a way through for the rushing waters, but without effect. As fast as the water tried to flow through the opening made by a charge of dynamite it froze again and plugged the hole through which it was attempting to escape.
Hastily improvised levees were thrown up, but the water outstripped the efforts of the builders. The lower part of St. Louis was flooded, and a great part of the population made homeless. Then low-lying lands beside the river were gradually submerged. In twenty-four hours there were calls for help all along the upper part of the Mississippi Valley. The rising water had flooded immense areas of cultivated land, and even larger areas were threatened. In another day a thousand square miles of crops were under water, and the loss in live stock was assuming formidable proportions. The new cold bomb in New York harbor had crept up to the Battery, as Teddy had foreseen. The Norfolk cold bomb had exploded, fortunately without loss of life. Gibraltar had witnessed three almost simultaneous blasts, and was again free of ice, but the whole world knew that it was at the mercy of Varrhus.