The latter, cased and guarded like the U-tube aft, exhibits another Fleury Ray, but inverted and more green than violet. Its function is to shunt the lift out of the gas, and this it will do without watching. That is all! A tiny pump-rod wheezing and whining to itself beside a sputtering green lamp. A hundred and fifty feet aft down the flat-topped tunnel of the tanks a violet light, restless and irresolute. Between the two, three white-painted turbine-trunks, like eel-baskets laid on their side, accentuate the empty perspectives. You can hear the trickle of the liquefied gas flowing from the vacuum into the bilge-tanks and the soft gluck-glock of gas-locks closing as Captain Purnall brings "162" down by the head. The hum of the turbines and the boom of the air on our skin is no more than a cotton-wool wrapping to the universal stillness. And we are running an eighteen-second mile.

I peer from the fore end of the engine-room over the hatch-coamings into the coach. The mail-clerks are sorting the Winnipeg, Calgary, and Medicine Hat bags: but there is a pack of cards ready on the table.

Suddenly a bell thrills; the engineers run to the turbine-valves and stand by; but the spectacled slave of the Ray in the U-tube never lifts his head. He must watch where he is. We are hard-braked and going astern; there is language from the control-platform.

"Tim's sparking badly about something," says the unruffled Captain Hodgson. "Let's look."

Captain Purnall is not the suave man we left half an hour since, but the embodied authority of the G. P. O. Ahead of us floats an ancient, aluminum-patched, twin-screw tramp of the dingiest, with no more right to the 5,000 foot lane than has a horse-cart to a modern town. She carries an obsolete "barbette" conning-tower—a six-foot affair with railed platform forward—and our warning beam plays on the top of it as a policeman's lantern flashes on the area sneak. Like a sneak-thief, too, emerges a shock-headed navigator in his shirt-sleeves. Captain Purnall wrenches open the colloid to talk with him man to man. There are times when Science does not satisfy.

"What under the stars are you doing here, you sky-scraping chimney-sweep?" he shouts as we two drift side by side. "Do you know this is a Mail-lane? You call yourself a sailor, sir? You ain't fit to peddle toy balloons to an Esquimaux. Your name and number! Report and get down, and be——!"

"I've been blown up once," the shock-headed man cries, hoarsely, as a dog barking. "I don't care two flips of a contact for anything you can do, Postey."

"Don't you, sir? But I'll make you care. I'll have you towed stern first to Disko and broke up. You can't recover insurance if you're broke for obstruction. Do you understand that?"

Then the stranger bellows: "Look at my propellers! There's been a wulli-wa down under that has knocked us into umbrella-frames! We've been blown up about forty thousand feet! We're all one conjuror's watch inside! My mate's arm's broke; my engineer's head's cut open; my Ray went out when the engines smashed; and ... and ... for pity's sake give me my height, Captain! We doubt we're dropping."

"Six thousand eight hundred. Can you hold it?" Captain Purnall overlooks all insults, and leans half out of the colloid, staring and snuffing. The stranger leaks pungently.

"We ought to blow into St. John's with luck. We're trying to plug the fore-tank now, but she's simply whistling it away," her captain wails.

"She's sinking like a log," says Captain Purnall in an undertone. "Call up the Banks Mark Boat, George." Our dip-dial shows that we, keeping abreast the tramp, have dropped five hundred feet the last few minutes.

Captain Purnall presses a switch and our signal beam begins to swing through the night, twizzling spokes of light across infinity.

"That'll fetch something," he says, while Captain Hodgson watches the General Communicator.