The turbines whistle reflectively. From the low-arched expansion-tanks on either side the valves descend pillarwise to the turbine-chests, and thence the obedient gas whirls through the spirals of blades with a force that would whip the teeth out of a power-saw. Behind, is its own pressure held in leash or spurred on by the lift-shunts; before it, the vacuum where Fleury's Ray dances in violet-green bands and whirled turbillions of flame. The jointed U-tubes of the vacuum-chamber are pressure-tempered colloid (no glass would endure the strain for an instant) and a junior engineer with tinted spectacles watches the Ray intently. It is the very heart of the machine—a mystery to this day. Even Fleury who begat it and, unlike Magniac, died a multi-millionaire, could not explain how the restless little imp shuddering in the U-tube can, in the fractional fraction of a second, strike the furious blast of gas into a chill grayish-green liquid that drains (you can hear it trickle) from the far end of the vacuum through the eduction-pipes and the mains back to the bilges. Here it returns to its gaseous, one had almost written sagacious, state and climbs to work afresh. Bilge-tank, upper tank, dorsal-tank, expansion-chamber, vacuum, main-return (as a liquid), and bilge-tank once more is the ordained cycle. Fleury's Ray sees to that; and the engineer with the tinted spectacles sees to Fleury's Ray. If a speck of oil, if even the natural grease of the human finger touch the hooded terminals Fleury's Ray will wink and disappear and must be laboriously built up again. This means half a day's work for all hands and an expense of one hundred and seventy-odd pounds to the G. P. O. for radium-salts and such trifles.
"Now look at our thrust-collars. You won't find much German compo there. Full-jewelled, you see," says Captain Hodgson as the engineer shunts open the top of a cap. Our shaft-bearings are C. M. C. (Commercial Minerals Company) stones, ground with as much care as the lens of a telescope. They cost £37 apiece. So far we have not arrived at their term of life. These bearings came from "No. 97," which took them over from the old "Dominion of Light," which had them out of the wreck of the "Perseus" aëroplane in the years when men still flew linen kites over thorium engines!
They are a shining reproof to all low-grade German "ruby" enamels, so-called "boort" facings, and the dangerous and unsatisfactory alumina compounds which please dividend-hunting owners and turn skippers crazy.
The rudder-gear and the gas lift-shunt, seated side by side under the engine-room dials, are the only machines in visible motion. The former sighs from time to time as the oil plunger rises and falls half an inch. 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."