Poynting's Theoretical Velocity Equation and a discussion of it are quoted from his original article. The equation is $X=(E-r_0{U}^2)\left(\frac{\mathrm{dy}}{\mathrm{dx}}\right)$, where $X=\mathrm{external}\mathrm{pressure}$, $U=\mathrm{resultant}\mathrm{relative}\mathrm{velocity}\mathrm{of}\mathrm{propagation}$, $E=\mathrm{elasticity}$, $\frac{\mathrm{dy}}{\mathrm{dx}}=\mathrm{volume}\mathrm{change}$ and $r_0=\mathrm{density}$. The corroborations obtained by Major Alter are stated to be: first, hearing the whistle of high velocity shells before they strike a target near the observer; second, calculations, based upon Poynting's equation, of the velocities measured by Mach, Berthelot and Wolf at various distances from the points of explosions. The calculated values agree with the observed values.

Observations taken in the laboratory did not show any change in the velocity of sound due to a spark source moving 8,550 cm. per second. The source consisted of a spark gap mounted on the end of a vane rotating 30 R. P. S. The spark was made to occur at the same point once in a revolution. Opposite points on the spherical wave front were located by two telephone transmitters and one receiver connected to a differential transformer. A minimum sound in the receiver indicated that the wave front arrived at the two transmitters simultaneously. The radii of the spherical waves measured varied from 190 to 260 centimeters. Normal room temperature and pressure prevailed.

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