Adding more mysteries to the DA white dwarf GD 394

We present spectroscopic and timing analyses of the hot DA white dwarf GD 3 94 showing abundance inhomogeneities across its surface. Lick Hamilton eche lle, International Ultraviolet Explorer (IUE), HST GHRS, and Hopkins Ultrav iolet Telescope (HUT) spectra show dominant Si III and Si IV features, whil e Extreme Ultraviolet Explorer (EUVE) spectra show evidence of a host of tr ace element opacities. We report the detection of Si III lambda 4552 triple t with a measured radial velocity of 27 km s(-1) in agreement with far ultr aviolet (FUV) line velocities, but indicating a silicon abundance (Si/H = 2 x 10(-5)) a factor of 10 larger than measured in the FUV range [Si/H = (2- 7) x 10(-6)]. Effective temperature measurements based on Lyman continuum ( EUVE) and Lyman line series (HUT) are systematically cooler (Delta T simila r to -4000 K) than measurements based on medium-dispersion Balmer line spec troscopy, an effect attributed to yet unidentified opacities. A timing anal ysis of EUVE: deep-survey and scanner time series, as well as spectrometer data, shows GD 394 to be variable in the extreme ultraviolet (EUV) with an amplitude of 25% and a period of 1.150 +/- 0.003 days. The EUV variability suggests abundance inhomogeneities in the atmosphere, and we explore differ ent models to explain its origin.