  Here within the basic design for a ground-based instrument for measuring the
magnitude of the Earth's time-retarded transverse gravitational vector
potential is described. The formula for the Earth's transverse vector potential
is derived from the known formula for the neoclassical time-retarded transverse
gravitational field (arXiv:0904.0383v2 [physics.gen-ph] 25May2010). The device
senses the relativistic shift in the frequency of laser-diode oscillators set
into circular motion at the tips of a two-arm rotor. The instrument employs
fiber optics and a digital electronic interferometer/spectrometer to measure
the effect of the relativistic time dilation on the frequency-modulated (FM)
harmonic amplitudes in the beat signals between the tip-diodes and a stationary
reference diode. The FM amplitudes depend on the orientation of the rotor. For
the vertical-east-west orientation with a rotor frequency of 73.9 Hz, the
predicted FM amplitudes for overtones at 148 Hz, 222 Hz, and 296 Hz are
respectively 7x10^-10 Hz, 4x10^-11 Hz, and 9x10^-11 Hz. The overtones in the
beat signals can be amplified and observed with a tunable FM digital audio
amplifier. The measured values for the harmonics of the vector potential can be
determined by back-calculating what the amplitudes must have been at the input
to the amplifier. The instrument can be used to establish the speed of the
Earth's gravitational field and to study the structure of the Earth's mantle
and outer core.
