  More than 36 years have passed since the discovery of the infrared excess
from circumstellar dust orbiting the white dwarf G29-38, which at 17.5 pc it is
the nearest and brightest of its class. The precise morphology of the orbiting
dust remains only marginally constrained by existing data, subject to
model-dependent inferences, and thus fundamental questions of its dynamical
origin and evolution persist. This study presents a means to constrain the
geometric distribution of the emitting dust using stellar pulsations measured
at optical wavelengths as a variable illumination source of the dust, which
re-radiates primarily in the infrared. By combining optical photometry from the
Whole Earth Telescope with 0.7-2.5 micron spectroscopy obtained with SpeX at
NASA's Infrared Telescope Facility, we detect luminosity variations at all
observed wavelengths, with variations at most wavelengths corresponding to the
behavior of the pulsating stellar photosphere, but towards the longest
wavelengths the light curves probe the corresponding time-variability of the
circumstellar dust. In addition to developing methodology, we find pulsation
amplitudes decrease with increasing wavelength for principal pulsation modes,
yet increase beyond approximately 2 microns for nonlinear combination
frequencies. We interpret these results as combination modes deriving from
principal modes of identical l values and discuss the implications for the
morphology of the warm dust. We also draw attention to some discrepancies
between our findings and theoretical expectations for the results of the
non-linearity imposed by the surface convection zone on mode--mode interactions
and on the behavior of the first harmonic of the highest-amplitude pulsation
mode.
