  The short-range order which remains when the isotropic to smectic-A
transition is perturbed by a gel of silica nanoparticles (aerosils) has been
studied using high-resolution synchrotron x-ray diffraction. The gels have been
created \textit{in situ} in decylcyanobiphenyl (10CB), which has a strongly
first-order isotropic to smectic-A transition. The effects are determined by
detailed analysis of the temperature and gel density dependence of the smectic
structure factor. In previous studies of the continuous nematic to smectic-A
transition in a variety of thermotropic liquid crystals the aerosil gel
appeared to pin, at random, the phase of the smectic density modulation. For
the isotropic to smectic-A transition the same gel perturbation yields
different results. The smectic correlation length decreases more slowly with
increasing random field variance in good quantitative agreement with the effect
of a random pinning field at a transition from a uniform phase directly to a
phase with one-dimensional translational order. We thus compare the influence
of random fields on a \textit{freezing} transition with and without an
intervening orientationally ordered phase.
