“But what is it?” he said.  “What is the meaning?”

Father Bechlin related how he had actually seen one of the troop of volors within five yards of the window; it was crowded with faces, he said, from stem to stern.  Then it had soared suddenly, and vanished in whorls of mist.

Percy shook his head, saying nothing.  He had no explanation.

“They are inquiring, I understand,” said Father Bechlin again.  “The conductor was at his instrument just now.”

There was nothing to be seen from the windows now.  Only, as Percy stared out, still dazed with the shock, he saw the cruel needle of rock wavering beneath as if seen through water, and the huge shoulder of snow swaying softly up and down.  It was quieter outside.  It appeared that the flock had passed, only somewhere from an infinite height still sounded a fitful wailing, as if a lonely bird were wandering, lost in space.

“That is the signalling volor,” murmured Percy to himself.

He had no theory—­no suggestion.  Yet the matter seemed an ominous one.  It was unheard of that an encounter with a hundred volors should take place, and he wondered why they were going southwards.  Again the name of Felsenburgh came to his mind.  What if that sinister man were still somewhere overhead?

“Eminence,” began the old man again.  But at that instant the car began to move.

A bell clanged, a vibration tingled underfoot, and then, soft as a flake of snow, the great ship began to rise, its movement perceptible only by the sudden drop and vanishing of the spire of rock at which Percy still stared.  Slowly the snowfield too began to flit downwards, a black cleft, whisked smoothly into sight from above, and disappeared again below, and a moment later once more the car seemed poised in white space as it climbed the slope of air down which it had dropped just now.  Again the wind-chord rent the atmosphere; and this time the answer was as faint and distant as a cry from another world.  The speed quickened, and the steady throb of the screw began to replace the swaying motion of the wings.  Again came the hoot, wild and echoing through the barren wilderness of rock walls beneath, and again with a sudden impulse the car soared.  It was going in great circles now, cautious as a cat, climbing, climbing, punctuating the ascent with cry after cry, searching the blind air for dangers.  Once again a vast white slope came into sight, illuminated by the glare from the windows, sinking ever more and more swiftly, receding and approaching—­until for one instant a jagged line of rocks grinned like teeth through the mist, dropped away and vanished, and with a clash of bells, and a last scream of warning, the throb of the screw passed from a whirr to a rising note, and the note to stillness, as the huge ship, clear at last of the frontier peaks, shook out her wings steady once more, and set out for her humming flight through space....  Whatever it was, was behind them now, vanished into the thick night.