'Sferics is the shortened term for atmospherics, natural radio-frequency emissions in the ionosphere, caused by electromagnetic energy radiated from nearby or distant lightning. These signals - resonant clicks and pops, called tweeks and bonks by scientists - occur in the audible range of humans and may be picked up by antennas and amplified for listening. They are best received at night, far from power lines. Occasionally, certain sferics get caught on and travel long distances along the magnetic flux lines around the earth, producing whistlers - downward-gliding signals which may last up to two or three seconds. My interest in sferics goes back to 1967, when I discovered in the Brandeis University Library a disc recording of ionospheric sounds by astrophysicist Millett Morgan of Dartmouth College. I experimented with this material, processing it in various ways - filtering, narrow band amplifying and phase-shifting - but I was unhappy with the idea of altering natural sounds and uneasy about using someone else's material for my own purposes. I wanted to have the experience of listening to these sounds in real time and collecting them for myself. When Pauline Oliveros invited me to visit the music department at the University of California at San Diego a year later, I proposed a whistler recording project. Despite two weeks of extending antenna wire across most of the La Jolla landscape and wrestling with homemade battery-operated radio receivers, Pauline and I had nothing to show for our efforts. About ten years later composer Ned Sublette, who was interested in radio waves of all kinds, recommended a book by Calvin R. Graf, Listen to Radio Energy, Light and Sound, which describe a simple method of building a large loop antenna with which to receive these natural phenomena. Sferics was recorded by the composer on August 27, 1981, in Church Park, Colorado. The sound material was collected continuously from midnight to dawn with a pair of homemade antennas and a stereo cassette tape recorder. At regular intervals the antennas were repositioned in order to explore the directivity of the propagated signals and to shift the stereo field.