Beneath them was only a t.i.tanic whirlpool of foaming waters in which only the curved top of the settling dome was visible for a moment as it sank slowly and ponderously downward, with a roar as of the roar of falling worlds. Buckling, collapsing, sinking, it vanished in the foam-wild sea with all the frog-men who for ages had ruled the second satellite, and with all those prisoners who had at the last dragged them down with them to death! Ripping off their helmets, with all the green men shouting crazily about them, Norman and Fellows and Hackett stared down at the colossal maelstrom in the waters that was the tomb of the masters of a world.

Then the depression's sides collapsed, the waters rushing together ...

and beneath them was but troubled, tossing sea....

Earth's great gray ball was overhead again and the sun was sinking again to the horizon when the three soared upward in the long, gleaming plane, its motor roaring. Norman, with Hackett and Fellows crowding the narrow cabin beside him, waved with them through its windows. For all around them were rising the flying-boats of the green men.

They were waving wildly, shouting their farewells, Sarja's tall figure erect at the prow of one. Insistent they had been that the three should stay, the three through whom the monstrous age-old tyranny of the frog-men had been lifted, but Earth-sickness was on them, and they had flown to where the plane lay still unharmed among the reeds, a hundred willing hands dragging it forth for the take-off.

The plane soared higher, motor thundering, and they saw the flying-boats sinking back from around them. They caught the wave of Sarja's hand still from the highest, and then that, too, was gone.

Upward they flew toward the great gray sphere, their eyes on the dark outlines of its continents and on one continent. Higher--higher--green land and gray tea receding beneath them; Hackett and Fellows intent and eager as Norman kept the plane rising. The satellite lay, a greenish globe, under them. And as they went higher still a rushing sound came louder to their ears.

"The edge of the satellite's atmosphere?" Fellows asked, as Norman nodded.

"We're almost to it--here we go!"

As he shot the plane higher, great forces smote it, gray Earth and green satellite and yellow sun gyrating round it as it reeled and plunged. Then suddenly it was falling steadily, gray Earth and its dark continent now beneath, while with a dwindling rushing roar its second satellite whirled away above them, pa.s.sing and vanishing.

Pa.s.sing as though, to Norman it seemed, all their strange sojourn on it were pa.s.sing; the frog-men and their mighty city, Sarja and their mad flight, the green men and the last terrific battle; all whirling away--whirling away.

HISTORIC EXPERIMENT PROVES EARTH'S ROTATION

The famous experiment which proves that the "earth do move" by letting the observer actually see it twisting underneath his feet, an experiment invented by the French mathematician Jean B. L. Foucault nearly a century ago was repeated recently under unusually impressive circ.u.mstances before an international scientific congress at Florence, Italy, the same city where Galileo once was persecuted for holding the same opinion.

From the center of the dome of the Church of Santa Maria di Fiore, Father Guido Alfani, director of the Astronomical Observatory, suspended a 200-pound weight on a wire 150 feet long. On the bottom of this weight was a tiny projecting point which traced a line on a table-top sprinkled with sand, as the great pendulum swung slowly back and forth. At a given signal Father Alfani set the pendulum to swinging. While the a.s.sembled scientists watched it, slowly the line traced across the sand table-top changed direction.

As Foucault proved long ago and as the watching scientists well knew, the table was being twisted underneath the pendulum by the rotation of the earth.

A REVOLUTIONARY AIRPLANE

A new airplane propeller has recently been patented by J. Kalmanson of Brooklyn, N. Y. Greater speed and marked saving in fuel is claimed for the invention, which may be attached to any type of airplane.

The device is in two parts, which may be used separately as front and rear propellers or combined into a single blade. The principle is that the front one acts to bring air to the other, giving the propeller more of a hold, so to speak, and greater power. This is accomplished by four air-spoons, one on each side of each blade of the propeller.

It is said that the device can double the speed of an airplane and raise it from the ground in ninety feet instead of the 200 feet most airplanes now require. It is also claimed that the new propeller will prevent the plane from making a nose drive unless the pilot forces it to do so, and enable it to make a safe landing within a short distance. Because of the increase in power and speed, the device would save a large amount of gasoline and oil, as well as guarding the motor from part of the strain on it.

The device is said to be also applicable to ships, the same principle operating in water as well as air.

Silver Dome

_By Harl Vincent_

[Ill.u.s.tration: _Orris led the way to a great underground city._]

[Sidenote: In her deep-buried kingdom of Theros, Phaestra reveals the amazing secret of the Silver Dome.]

In a secluded spot among the hills of northern New Jersey stood the old DeBost mansion, a rambling frame structure of many wings and gables that was well-nigh hidden from the road by the half-mile or more of second-growth timber which intervened. High on the hill it stood, and it was only by virtue of its alt.i.tude that an occasional glimpse might be obtained of weatherbeaten gable or partly tumbled-down chimney. The place was reputed to be haunted since the death of old DeBost, some seven years previously, and the path which had once been a winding driveway was now seldom trod by human foot.

It was now two years since Edwin Leland bought the estate for a song and took up his residence in the gloomy old house. And it had then been vacant for five years since DeBost shot himself in the northeast bedroom. Leland's a.s.sociates were sure he would repent of his bargain in a very short time, but he stayed on and on in the place, with no company save that of his man-servant, an aged hunch-back who was known to outsiders only as Thomas.

Leland was a scientist of note before he buried himself in the DeBost place, and had been employed in the New York research laboratory of one of the large electrical manufacturers, where he was much admired and not a little envied by his fellow workers. These knew almost nothing of his habits or of his personal affairs, and were much surprised when he announced one day that he had come into a sizable fortune and was leaving the organization to go in for private research and study. Attempts to dissuade him were of no avail, and the purchase of the DeBost property followed, after which Leland dropped from sight for nearly two years.

Then, on a bl.u.s.tery winter day, a strange telephone call was received at the laboratory where he had previously worked. It was from old Thomas, out there in the DeBost mansion, and his quavering voice asked for Frank Rowley, the genial young engineer whose work had been most closely a.s.sociated with Leland's.

"Oh, Mr. Rowley," wailed the old man, when Frank responded to the call, "I wish you would come out here right away. The master has been acting very queerly of late, and to-day he has locked himself in his laboratory and will not answer my knocks."

"Why don't you break in the door?" asked Frank, looking through the window at the snow storm that still raged.

"I thought of that, Mr. Rowley, but it is of oak and very thick.

Besides, it is bound with steel or iron straps and is beyond my powers."

"Why not call the police?" growled Frank. He did not relish the idea of a sixty or seventy mile drive in the blizzard.

"Oh--no--no--no!" Old Thomas was panicky at the suggestion. "The master told me he'd kill me if I ever did that."

Before Frank could formulate a reply, there came a sharp gasp from the other end of the line, a wailing cry and a thud as of a falling body; then silence. All efforts to raise Leland's number merely resulted in "busy" or "line out of order" reports.

Frank Rowley was genuinely concerned. Though he had never been a close friend of Leland's, the two had worked on many a knotty problem together and were in daily contact during the nearly ten years that the other man had worked in the same laboratory.

"Say, Tommy," said Frank, replacing the receiver and turning to his friend, Arnold Thompson, who sat at an adjoining desk, "something has happened out at Leland's place in Suss.e.x County. Want to take a drive out there with me?"

"What? On a day like this? Why not take the train?"

"Don't be foolish, Tommy," said Frank. "The place is eight miles from the nearest station, which is a flag stop out in the wilds. And, even if you could find a cab there--which you couldn't--there isn't a taxi driver in Jersey who'd take you up into those mountains on a day like this. No, we'll have to drive. It'll be okay. I've got chains on the rear and a heater in the old coupe, so it shouldn't be so bad. What do you say?"

So Tommy, who usually followed wherever Frank led, was prevailed upon to make the trip. He had no particular feeling for Leland, but he sensed an adventure, and, in Frank's company, he could ask for no more.

Frank was a careful driver, and three hours were required to make the sixty-mile journey. Consequently, it was late in the afternoon when they arrived at the old DeBost estate. It had stopped snowing, but the drifts were deep in spots, and Frank soon found that the car could not be driven through the winding path from the road to the house. So they left it half buried in a drift and proceeded on foot.

It was a laborious task they had undertaken, and, by the time they set foot on the dilapidated porch, even Frank, husky and athletic as was his build, was puffing and snorting from his exertions. Little Tommy, who tipped the scales at less than a hundred and twenty, could hardly speak. They both were wet to the waist and in none too good humor.

"Holy smoke!" gasped Tommy, stamping the clinging snow from his sodden trouser legs and shoes, "if it snows any more, how in Sam Hill are we going to get out of this place?"

"Rotten trip I let you in for Tommy," growled Frank, "and I hope Leland's worth it. But, darn it all, I just had to come."

"It's all right with me, Frank. And maybe it'll be worth it yet.

Look--the front door's open."