The gyroscope has been used for navigational purposes since the 1920’s, its accuracy improving as technology advanced. Today’s state-of-the-art gyroscopes use two counter-propagating beams of continuous wave (CW) light in a ring configuration and take the difference frequency between the two beams to be a measure of the rotation rate. The ring can exists in any propagating media such as an optical fiber or a bulk optical ring.

The principle behind the laser gyro is known as the Sagnac effect.[6]  This effect is the phase shift induced by a light beam as it completes a loop, when the plane of the loop is given a rotation. The phase shift occurs because the length of the path changes due to the rotation.

As Richard B. Johnson, author of Abominable Firebug [3]  discovered, one does not need to use light. One could use sound waves in air. Of course, the velocity of the sound is highly dependent upon temperature so such a device would be difficult to calibrate. Since the velocity of sound is very slow relative to the speed of light, the time for its phase to change because of rotation is greatly increased. This makes such a rate gyro quite sensitive. The speed of sound at sea level on a standard day is about 340 meters per second. If we created a circular sound column 340 meters in length, a 1 kHz tone would undergo 1,000 complete cycles during its passage through the circular pipe. Of course, 340 meters is an impractical length. However, 34 meters is not. One could use a 10 kHz tone instead, and still obtain 1,000 complete cycles. In this case, the circulating sound would be affected by rotation for 1/10th of a second round-trip time instead of one second. Since the propagating sound is electrically generated, there is no need to use an interferometer to detect phase differences. Just directly compare the output signal phase with the input signal phase. This is what Johnson’s acoustic rate gyroscope did.

In 1959, not much was published about laser operation. Much less was known about laser gyroscopes.[1]  The first working laser was made by Theodore H. Maiman in 1960.[4]  The United States was deeply involved in the Cold War and anything that might be useful for ICBM technology was a closely guarded secret. As a sixteen-year-old High School student at Boston’s Roslindale High, I started a science fair project to build a gyroscope that had no moving parts. I did not know anything about lasers and, in fact, had never heard of them. However, I had learned about rate-gyroscopes from textbooks, and I was determined to make one that did not use any moving parts.

I decided to make a column of air propagate sound going around and around like the spinning momentum wheel of a mechanical gyroscope. I assumed there would be some Doppler effect that I could measure electronically, to indicate the change in direction the device was pointing. In fact, I did not know what I was doing. I was actually using the Sagnac effect, used nowadays in laser and fiber-optic gyroscopes. At the time, I did not know that this was “top secret” stuff. The device worked and was, in fact sensitive enough to detect the rotation of the earth. The fact that I did not know why it worked was never even considered because I assumed that it worked because of ordinary Doppler effects. Many years after its invention, researchers at Maine University, Le Mans, France, published a paper describing the effects of inertia forces on sound fields in closed spaces. [9] This paper described the underlying principles of operation for this device.
It consisted of a roll of plastic tubing with piezoelectric “earphone” transducers at both ends. An audio-frequency signal fed into one end, and received at the other. The phase between the input and output signal was measured. I used vacuum-tube circuits for the sound source, the amplifiers, and the phase detectors. The device was very impressive and my physics teacher arranged for me to demonstrate my invention to Sperry, [5]  the gyroscope company. He thought that they might give me a scholarship to MIT or some other university like Princeton or Harvard.

They must have been impressed, but rather than giving me a scholarship to MIT, they presented me with a “Cease and Desist Order” from a Federal District Court in Islip, Long Island. Federal agents came to school, packed up my stuff into boxes labeled “evidence,” and took the science fair project away! I write more details about this in my book, Abominable Firebug.[3]  With only two weeks left to complete another project, I still won the “Rossie High” competition and the opportunity to compete state-wide. Of course, I stayed away from nuclear missiles and such.

According to the cited reference,[2]  a gyroscope first detected the earth’s rotation on January 7, 1963. Methinks this is an example of the continuous rewrite of history. It happened in 1959 in a High School physics laboratory off Roslindale Square in Boston, but the government didn’t want you to know.[7,8] 

   1. Laser gyroscope article on Wikipedia
   2. “From the Luminiferous Ether to the Boeing 757: A History of the Laser Gyroscope,” Donald MacKenzie, Technology and Culture, Vol. 34, No. 3 (Jul., 1993), pp. 475-515
   3. Abominable Firebug ISBN 0-595-386667-9
   4. Maiman, T.H. (1960) “Stimulated Optical Radiation in Ruby” Nature, 187 4736, pp. 493-494
   5. Sperry Gyroscope article on Wikipedia
   6. Sagnac effect article on Wikipedia
   7. About court orders to hide discoveries
   8. More about this science fair and the gyroscope
   9. Effect of inertial forces on acoustic fields in a closed space

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