Professor Rudnick and his colleagues built the most powerful siren ever conceived to date. It made what was, as far as anybody knew, the loudest continuous sound ever heard on earth up to the time: 175 dB, some 10,000 times as strong as the ear-splitting din of a large pneumatic riveter. The frequency range of this enormous howl was from about 3,000 cycles per second to 34, 000 cps, in the ultrasonic range.

Strange things happened in this nightmarish sound field. If a man put his hand directly in the beam of a sound, he got a painful burn between the fingers. When the siren was aimed upwards, 3/4 inch marbles would float lazily above it at certain points in the harmonic field, held up and in by the field, Prof. Rudnick could make pennies dance on a silk screen with chorus-like perfection while balancing another penny on its edge. A cotton wad held in the field would burst into flame in about 6 seconds. " To satisfy a skeptical colleague", reports Prof. Rudnick, " we lit his pipe by exposing the open end of the bowl to the field" (1)