Used for everything from flying saucer engines and killer robot noises to the sting of the Green Hornet on radio and building suspense in thriller films, the theremin has earned a place of admiration among sci-fi fans. Read on to learn more about this amazing and mysterious musical instrument.

The theremin was invented by Russian physicist Lev Sergeyvich Termen (1896-1993) in 1919. While working on an unrelated instrument, he discovered that moving his hands near two large metal plates caused a change in a signal coming from the apparatus. After examining the effect, he developed the instrument that would soon turn him into an overnight success.

Professor Termen began to demonstrate the Aetherphon, as he called it, around Russia in 1921 for both public and private audiences, including Lenin himself! He debuted the instrument in Europe in 1927 and came to the United States shortly afterwards. By then, his name had been Anglicized to "Leon Theremin" (a French-sounding name apparently added an air of sophistication to the young scientist), and the instrument had become known as "the theremin."

In 1929, he sold the patent rights to Radio Corporation of America (RCA) and for the first time, theremins were produced commercially. RCA built theremins for one year and manufactured only 500. The instruments were said to be playable by "anyone who can hum a tune." The original RCA theremins have become collector's items and many are viewable in museums around the world today. The basic design of the theremin was simple enough that several electronic and radio hobbiest magazines published schematics for theremins througout the years.

Following the donation of a brownstone in Manhattan by the Rosen family, Professor Theremin set up a studio/laboratory and lived in the United States for nearly 10 years. During this time, he worked on new inventions and gave lessons on the theremin. One student, Clara Rockmore, stood out among the others as a shining star. A former child prodigy violinist, she played the theremin with the seriousness and dedication due any other classical instrument. She is known as the only person to truly master the theremin and is considered a virtuoso. Ms. Rockmore participated in public performances with both the conventional theremin and with a dance-style version of the instrument called the terpsitone.

What happened next may remind Sci-Fi fans of a plot to the X-Files! One day in 1938, a group of men in dark suits appeared at the lab in Manhattan and whisked Leon Theremin away without any explanation. Everyone who had known him was baffled, and after years of luckless searching assumed he was dead. In actuality, he had been taken back to the Soviet Union and put to work in a labor camp. It was not until many years later during a trip to the country that Clara Rockmore learned he was still alive. In 1991, Professor Theremin came to the United States for a presentation at Stanford University and was finally reunited with Clara Rockmore. Footage of this event can be seen in the documentary film, "Theremin: An Electronic Odyssey" by Steven M. Martin.

The theremin is played by moving one's hands near two large metal antennas. One antenna controls volume (moving closer to the volume antenna softens the sound), and the other controls pitch (moving closer to the pitch antenna increases the pitch).

The basic principle behind the theremin is known as heterodyning - the mixing of two signals of different frequencies and extracting their difference. The pitch circuit of the theremin uses two radio-frequency oscillators, one fixed and one variable, to create this effect. Moving the hands near the pitch antenna changes the speed of the variable oscillator, and the difference between the two comes out as a musical note. The volume circuit works in a similar manner. Most theremins have a range of 3-5 octaves.

The original theremins were built using vacuum tubes. In 1961, Robert Moog published one of the very first transistorized theremin schematics in Electronics World Magazine. Some modern theremins use hybrid digital/analog electronics and some even include MIDI output!

The theremin was used in many science fiction films of the 50's and 60's. Among those are:

• Rocketship X-M (1950) - This film starred Llyod Bridges and was scored by Ferde Grofe. A group of astronauts are diverted to Mars while on a trip to the moon. While they walk around the surface of the planet, theremins wail in the background. This 30-minute sequence is perhaps the longest continuous theremin appearance on film.

• The Day the Earth Stood Still (1951) - This film was responsible for the famous words, "Klaatu... barada... nikto..." The theremin was used extensively in the score by Bernard Herrmann. Listen for the theremin as the killer robot Gort punishes humanity.

• It Came from Outer Space - Another classic film making use of the theremin. As the one-eyed blob monster takes the form of its human victims, the theremin wails out like a scream.

A newsgroup, alt.music.makers.theremin is also available. Here, you can find discussions about playing techniques, live performance, history, and construction tips.