This paper is an account of an experiment designed to determine the binding energy of the deuteron by a method which is relatively insensitive to uncertainties in the energy-range relation for protons of low energy. The protons, produced by the disintegration of deuterium by Th C″ gamma-radiation, were observed in a low-pressure cloud chamber in a strong magnetic field. The curvatures of the tracks allowed the calculation of the corresponding kinetic energies. The final value of the binding energy as got by this experiment is VB=2.17+/- 0.05x106 electron-volts, which is in excellent agreement with the values previously got by Bethe (from the data of Chadwick, Feather and Bretscher) and by J. R. Richardson and Emo.