Acoustical detection of electrical discharges was perhaps the earliest technology used by man as he became aware of lightning flashes and the associated sound of thunder during rainstorms. Presumably, for millions of years man knew that the sound of thunder gave an early warning of an approaching storm (Lucretius (95-55 BC) was aware that lightning is seen before thunder is heard [1]). But not until more recent history, when man could record time accurately and measure the velocity of sound waves in air (Marsenne (1588–1648) measured the speed of sound in air using a pendulum and reported a value of 316.46 m/s [2].), could he estimate the distance to the lightning discharge that caused the sound waves (DeLisle [3] in 1738). With the dawn of the electrical age (circa 1874 [4]), it was apparent that high-voltage sparks in air produced acoustic emissions in a similar fashion, but on a much reduced scale, to lightning. As increasingly higher voltages were used, electrical coronas at highly stressed regions on electrical apparatus, such as the uninsulated conductors of high-voltage power lines, could be seen by eye in the dark, and their associated acoustic emissions heard by ear.