THE SECOND SHELL By JACK WILLIAMSON _By the Author of "The Alien Intelligence," "The Girl from Mars"_ [Illustration: JACK WILLIAMSON] _Here the well-known author of "The Alien Intelligence" and other thrilling stories presents his latest symphony, a fine piece of aerial fiction._ _Few authors have Jack Williamson's knack to pack their stories with so much adventure and with so much imaginative science. And while it may be fantastic today, most of it we know, sooner or later, will have become reality._ _All scientists for decades have been wondering what the mysterious Heaviside Layer is. Radio engineers know of the Heaviside Layer from its effect on radio waves. It is very much of a fact, yet no one has ever been able to get near it, due to its distance above the surface of the earth, and till we have penetrated it, we cannot be sure what lies above it._ _We know you will enjoy the present story, which easily bears re-reading from time to time._ [Transcriber's Note: This etext was produced from Air Wonder Stories November 1929 Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] It was two o'clock in the morning of September 5, 1939. For a year and a half I had been at work on the San Francisco _Times_. I had come there immediately after finishing my year's course at the army officers' flying school at San Antonio, on the chance that my work would lead me into enough tong wars and exciting murder mysteries to make life interesting. The morning edition had just been "put to bed" and I was starting out of the office when the night editor called me to meet a visitor who had just come in. The stranger came forward quickly. Roughly clad in blue shirt and overalls, boots, and Stetson, he had the bronze skin, clear eyes, and smooth movements of one who has spent his life out-of-doors. He stopped before me and held out his hand with a pleasant smile. I saw that his hair was gray; he was a little older than I had thought at first--fifty, perhaps. I liked the fellow instinctively. "Robert Barrett?" he questioned in a pleasant drawl. I nodded. "I'm Bill Johnson," he said briefly. "I want to see you. Secret Service business. _Sabe?_" He let me glimpse a badge, and we walked out into the night. As we started down the silent street it occurred to me that I had heard of this man before. "Are you the William Johnson who unearthed the radio station of the revolutionaries in Mexico in 1917?" "I guess so. I've been in Mexico thirty years, and I've helped Uncle Sam out a time or two. It's a case like that one, or worse, that I'm up here to see about now. I need a partner. I've been told about you. Are you game for a little adventure?" "You've found your man." "They call you 'Tiger Bob Barrett,' don't they?" he said irrelevantly.