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We have determined column densities of H I and/or H_2 for sight lines in theMagellanic Clouds from archival HST and FUSE spectra of H I Lyman-alpha and H_2Lyman-band absorption. Together with some similar data from the literature, wenow have absorption-based N(H I) and/or N(H_2) for 285 LMC and SMC sight lines(114 with a detection or limit for both species) -- enabling more extensive,direct, and accurate determinations of molecular fractions, gas-to-dust ratios,and elemental depletions in these two nearby, low-metallicity galaxies. Forsight lines where the N(H I) estimated from 21 cm emission is significantlyhigher than the value derived from Lyman-alpha absorption (presumably due toemission from gas beyond the target stars), integration of the 21 cm profileonly over the velocity range seen in Na I or H_2 absorption generally yieldsmuch better agreement. Conversely, N(21 cm) can be lower than N(Ly-alpha) byfactors of 2--3 in some LMC sight lines -- suggestive of small-scale structurewithin the 21 cm beam(s) and/or some saturation in the emission. The meangas-to-dust ratios obtained from N(H_tot)/E(B-V) are larger than in our Galaxy,by factors of 2.8--2.9 in the LMC and 4.1--5.2 in the SMC -- i.e., factorssimilar to the differences in metallicity. The N(H_2)/E(B-V) ratios are moresimilar in the three galaxies, but with considerable scatter within eachgalaxy. These data may be used to test models of the atomic-to-moleculartransition at low metallicities and predictions of N(H_2) based on comparisonsof 21 cm emission and the IR emission from dust.

Interstellar H I and H_2 in the Magellanic Clouds: An Expanded Sample Based on UV Absorption-Line Data