Supersonic Satellites and Velocity

With increasing path length in a Pierce acoustic interferometer, minor peaks, or "satellites," were found to develop in the curves which correlate ($I_P-I_B$), the excess of plate current over bias current, and $x$, the mirror position. Several such curves are given. Evidence that these satellites are caused by multiple reflection is presented. The acoustic velocity as determined by these satellites, differs by less than 0.06 percent from the theoretical value, $V={\left(\frac{\gamma p}{d}\right)}^{\frac{1}{2}}$, whereas the major peaks yield a velocity which, in every case, exceeds the theoretical value by more than 0.5 percent. Apparently the velocity approaches a limiting minimum value with decreasing intensity, but is independent of frequency.