It must have been dull work, flying from the Falkland Islands to South Shetland, deafened by roaring jets and blinded by the frightful gales that swirled around Cape Horn, and for variety he had the constant ticking of his scintillometer telling him how closely he was approaching the southern boundary of the Atomic Curtain, quite narrow there, encompassing the Cape itself and the wild seas immediately beyond. Dull work? I remember O'Hara's first letter: "The black sky meets the blacker water upon a horizon even more intensely black, a horizon that is a ribbon of mourning constantly below the level of my eyesight, as if these were dead seas and dead heavens. But the coloration is deceptive, for they are not dead. The howling violence that must have been the planet's birthing wail still echoes here, the raging winds that must have screeched throughout infinity when Earth ripped loose from the Sun--and beyond, ten miles ahead of me, perhaps, the Wall of Death invisibly stands shimmering. "One second's miscalculation at the speed I fly and I'd be into it. Freezing one instant, roasted to the bone the next. How thick is that wall? The guess that we credit oftenest is twelve miles. A scant twelve miles of radioactivity, and I could fly that far in the time it would take you to snap shut the fingers of your hand--perhaps my craft on its momentum would plunge through. I think it would. I think I could aim it for the southern tip of South America, and by the time that you could walk across the editorial room there at the _Observer_ in London, I would have smashed across the Atomic Curtain and landed on that coast that once was Patagonia. Isn't that a challenge? A terrific challenge, to be the first within two hundred and seventy years to reach the two lost continents! But it has the undeniable drawback that I would be dead, and so could not gloat like stout Balboa on a peak in Darien. "I saw the Curtain doing its merry routine one day last week. I was flying quite low, not a hundred feet above the surface of the sea, making a customary check upon the water's radioactivity. We do this every flight, to check upon the contamination of the water, which usually is quite constant, flowing out from below the Curtain a distance of fifty miles but decreasing in activity with an almost mathematical precision. Yet when there is a really powerful gale blowing southward or westward from the Curtain, from the tip of what once was called Chile or Argentina, both now encompassed by the Curtain, the surface currents sometimes are reversed from the Cape--the fabled Cape Horn of early mariners--and the contamination flows much further toward the Antarctic before it diffuses.