The decay of imprisoned resonance radiation in mercury has been studied using delayed-coincidence techniques. It is characterized by two exponentially decaying components, whose relative amplitudes depend on the direction of linear polarization of the incident radiation. When this direction makes an angle of 54.7° to the direction of observation, only one component is observed. Classical and quantum-mechanical theories are presented which show that the geometry of the scattering cell plays an important role at low atomic densities. Experimental values are presented for the average degree of coherence transferred in the scattering process and for the natural lifetime of the 63P1 state of mercury.