  About a dozen measurements of Newton's gravitational constant, G, since 1962
have yielded values that differ by far more than their reported random plus
systematic errors. We find that these values for G are oscillatory in nature,
with a period of P = 5.899 +/- 0.062 yr, an amplitude of (1.619 +/- 0.103) x
10^{-14} m^3 kg^{-1} s^{-2}, and mean-value crossings in 1994 and 1997.
However, we do not suggest that G is actually varying by this much, this
quickly, but instead that something in the measurement process varies. Of other
recently reported results, to the best of our knowledge, the only measurement
with the same period and phase is the Length of Day (LOD - defined as a
frequency measurement such that a positive increase in LOD values means slower
Earth rotation rates and therefore longer days). The aforementioned period is
also about half of a solar activity cycle, but the correlation is far less
convincing. The 5.9 year periodic signal in LOD has previously been interpreted
as due to fluid core motions and inner-core coupling. We report the G/LOD
correlation, whose statistical significance is 0.99764 assuming no difference
in phase, without claiming to have any satisfactory explanation for it. Least
unlikely, perhaps, are currents in the Earth's fluid core that change both its
moment of inertia (affecting LOD) and the circumstances in which the
Earth-based experiments measure G. In this case, there might be correlations
with terrestrial magnetic field measurements.
