Not in bursts of flame did they go plunging down the depths, gyrating like mad comets with long smoke-trailers and redly licking manes of fire.  Not in shattered fragments did they burst and plumb the abyss.  No; quite intact, unharmed, but utterly powerless they fell.

Some spiraled down, like dead leaves twirling in autumnal breezes, with drunken yaws and pitches.  Others in long slants volplaned toward the hidden sea, miles below the cloud-plain.  A few pitched over and over, or slid away in nose-dives and tail-spins.  But one and all, as they crossed what seemed an invisible line drawn out there ahead of the onrushing Eagle of the Sky, bowed to some mysterious force.

It seemed almost as if Nissr were the center of a vast sphere that moved with her—­a sphere through which no enemy could pass—­a sphere against the intangible surface of which even the most powerful engines of the air dashed themselves in vain.

And still, as others and still others came charging up to the attack like knights in joust, they fell.  One by one the white wool cushions of the cloud, gold-broidered by the magic needles of the sun, received them.  One by one they faded, vanished, were no more.

So, all disappeared.  Between a hundred and a hundred and twenty-five planes were silently, swiftly, resistlessly sent down in no more than twenty minutes, while the watchers stood there in the gallery, fascinated by the wondrous precision and power of this new and far-outflung globe of protection.

And again the blood-red morning sky grew clear of attackers.  Again, between high heaven’s black vault and the fantastic continent of cloud below, nothing remained but free vacancy.  The Master smiled.

“Vibrations, my dear Major!” said he.  “Neutralize the currents delivered by the magnetos of hostile planes to their spark-plugs, and you transform the most powerful engines into inert matter.  Not all the finely adjusted mechanism in the world, nor the best of petrol, nor yet the most perfect skill is worth that,” with a snap of the strong fingers, “when the spark dies.

“My device is the absolute ruler of whatever spark I direct it against.  Our own ignition is screened; but all others within the critical radius become impotent.  So you recognize, do you not, the uselessness of machine-guns?  The groundlessness of any fears about the Air Patrol’s forces?”

“Lord, but this is wonderful!” Bohannan ejaculated.  “If we’d only had this in the Great War, the Hun would have been wiped out in a month!”

“Yes, but we didn’t have it,” the Master smiled.  “I’ve just finished perfecting it.  Put the last touches on it hardly twenty-four hours ago.  If there’s ever another war, though—­ah, see there, now!  Here comes one lone, last attacker!”

He pointed.  Far at the edge of empty cloudland, now less blood-stained and becoming a ruddy pink under the risen sun, a solitary aerial jouster had grown visible.