Abstract
Growth of a magnetic field given to the zero-field state of a Bullard-Gellman dynamo model is studied. Reaction of electromagnetic origin to the fluid motion is completely ignored. A steady state seems to be reached within a time comparable with that of free decay of the magnetic field, say several thousand years, for the earth's core. A more complete study, in which an equation of motion is taken into account, will be made in the second paper.
