The pits of gloom about us begin to fill with very faintly luminous films--wreathing and uneasy shapes. One forms itself into a globe of pale flame that waits shivering with eagerness till we sweep by. It leaps monstrously across the blackness, alights on the precise tip of our nose, pirouettes there an instant, and swings off. Our roaring bow sinks as though that light were lead--sinks and recovers to lurch and stumble again beneath the next blow-out. Tim's fingers on the lift-shunt strike chords of numbers--1:4:7:--2:4:6:--7:5:3, and so on; for he is running by his tanks only, lifting or lowering her against the uneasy air. All three engines are at work, for the sooner we have skated over this thin ice the better. Higher we dare not go. The whole upper vault is charged with pale krypton vapours, which our skin friction may excite to unholy manifestations. Between the upper and lower levels--5000 and 7000, hints the Mark Boat--we may perhaps bolt through if... Our bow clothes itself in blue flame and falls like a sword. No human skill can keep pace with the changing tensions. A vortex has us by the beak and we dive down a two-thousand foot slant at an angle (the dip-dial and my bouncing body record it) of thirty-five. Our turbines scream shrilly; the propellers cannot bite on the thin air; Tim shunts the lift out of five tanks at once and by sheer weight drives her bullet wise through the maelstrom till she cushions with jar on an up-gust, three thousand feet below. “Now we've done it,” says George in my ear: “Our skin-friction, that last slide, has played Old Harry with the tensions! Look out for laterals, Tim; she'll want some holding.” “I've got her,” is the answer. “Come up, old woman.” She comes up nobly, but the laterals buffet her left and right like the pinions of angry angels. She is jolted off her course four ways at once, and cuffed into place again, only to be swung aside and dropped into a new chaos. We are never without a corposant grinning on our bows or rolling head over heels from nose to midships, and to the crackle of electricity around and within us is added once or twice the rattle of hail--hail that will never fall on any sea. Slow we must or we may break our back, pitch-poling. “Air's a perfectly elastic fluid,” roars George above the tumult. “About as elastic as a head sea off the Fastnet, ain't it?”