Introduction

There has been extensive theoretical and observational interest in establishing what fraction of the total ionizing luminosity from the stellar disk of the Milky Way and other galaxies escapes into the halo and the intergalactic medium (e.g., Miller & Cox 1993; Dove & Shull 1994; Leitherer & Heckman 1995). Diffuse ionized gas between HII regions in half a dozen well studied galaxies suggests that a significant fraction escapes to ionize the ambient ISM (e.g. Hoopes, Walterbos & Greenawalt 1996; Ferguson et al. 1996). Broadly speaking, if the optical depth at the Lyman limit is , these observations require on the scale of the diffuse disk gas. The vertically extended Reynolds Layer requires that to explain the observed line emission (Reynolds 1990). We now show that the observed emission measures at the distance of the Magellanic stream (0.5-1 cm pc in the MS II-IV clumps) are consistent with ionization by the Galactic disk (Weiner & Williams 1996; q.v. Bland-Hawthorn 1997), providing perpendicular to the disk. More detailed calculations are given in Bland-Hawthorn & Maloney (1996).

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