A new source of electromagnetic excitation of the Moon is identified. It is distinct from the known spherical transverse electric (TE) mode forced by time variations of the interplanetary magnetic field. This new source is a consequence of the extension of the diamagnetic cavity field into the lunar interior and is detected on the sunlit lunar surface as a strong induction signal, directed preferentially east and west, and superimposed upon the global TE mode. The induction signal is hypothesized to be the time-dependent part of the diamagnetic cavity fringing field within the Moon. The signal results from overall expansion and contraction of the lunar cavity measured here in the frequency range of 10-5?f?10-4 Hz. This ''breathing'' mode of the Moon-cavity system is in turn based upon large scale hydromagnetic pressure variations of the solar wind. Confinement of the cavity fringing field to the lunar interior results in the lines of force being folded over just above the lunar surface and swept downstream above a region of reduced field intensity in the cavity walls. This is consistent with earlier observation. The associated current layer extends upstream over the face of the Moon. The diamagnetic contribution to induction seen on the sunlit lunar surface also suggests a resolution of the long-standing difference between the excess induction noted experimentally on the darkside of the Moon (Kuckes, 1974) and that computed from TE mode theory.