Many authors have considered a gravitational origin of the magnetic field of celestial bodies. In this approach the Wilson-Blackett or Schuster hypothesis has been playing an important role for more than a century. This hypothesis connects the magnetic moment M of the body to its angular momentum S. In this paper the gravitomagnetic ratios M/S deduced from observational data for a series of very different rotating massive bodies are compared with predicted values.

The considered magnetic moments M and corresponding angular moments S of the rotating bodies range from metallic cylinders in the laboratory, moons, planets, pulsars, white dwarfs and Ap stars to the Milky Way. Furthermore, the lightest neutrino of mass m₁ has also been added to the list.

For huge intervals of more than 100 decades for the values of M and S the so-called Wilson-Blackett relation seems to be approximately valid. On smaller scales deviations become more manifest. Effects from electromagnetic origin may be responsible for these deviations.