The origin of stellar magnetic fields is still uncertain. For decades a fossil field mechanism has been postulated for white dwarfs, based on magnetic flux conservation of Ap or Bp stars. Later on, dynamo action in the common envelope of binary systems has been proposed as an origin of magnetic fields in white dwarfs. Recently, dynamo action in the convective region of isolated white dwarfs has been considered as an explanation.

In this work a gravitational origin for the magnetic fields of rotating massive bodies is reinvestigated. This approach has led to the so-called Wilson-Blackett law that predicts a dipolar magnetic field for all rotating electrically neutral bodies. A short review of the history of this law is given. The validity of the Wilson-Blackett formula for white dwarfs will be examined in this work.

Results are given for ten isolated white dwarfs, eleven AM Herculis systems, one DQ Herculis system and two double-white-dwarf binaries. In most cases only approximate agreement with the predictions of the Wilson- Blackett formula is found. Contributions from electromagnetic origin may be responsible for the deviations. The results for white dwarfs are compared with corresponding classes of pulsars.