[en] Orthopositronium (o-Ps), formed on the cone of a channel electron multiplier by 400-eV positrons, is shown to diffuse quickly into an MgO-coated evacuated chamber with energies up to 0.8 +- 0.2 eV. The decay rate of o-Ps is measured to be 7.09 +- 0.02 μsec^-1, where the error is due principally to systematic effects. This result is interpreted to be the first direct measurement of the vacuum decay rate of the o-Ps. It is in disagreement with the theoretical value of 7.242 +- 0.008 μ sec^-1 and previous experiments in gases as well