Dichroism experiments with 150 fs time resolution on anthracene in benzyl alcohol are presented as a function of viscosity from 14.4 cP (274 K) to 2.7 cP (329 K). These measurements test a qualitative prediction of the viscoelastic picture of liquid dynamics, specifically that earlier "inertial" dynamics have a viscosity independent rate, whereas later "diffusive" dynamics have a rate directly proportional to viscosity. This paper focuses on two components of the dichroism decay that are assigned to rotational motion. A third component is assigned to electronic-state solvation and is analyzed in a companion paper [J. Chem. Phys. 115, 4231 (2001)]. The longest component is due to rotational diffusion and is very well described by a hydrodynamic model with slip boundary conditions. A fast decay component in the subpicosecond region is found and shown to have a viscosity-independent rate. It is assigned to inertial rotation by comparison to the computer simulations of Jas et al. [J. Chem. Phys. 107, 8800 (1997)]. Inertial rotation extends out to at least 1 ps, longer than the range commonly assumed for inertial dynamics. Over much of this range, the inertial rotation is not free-rotor-like, but is strongly modified by interaction with the solvent. The inertial rotation also accounts for the "missing" anisotropy found when the rotational diffusion fits are extrapolated to zero time.