  All gasdynamical models for the evolution of gaseous content of galaxies
assume that cooling from the hot, virialized phase to the cold phase occured
through some sort of thermal instability. Subsequent formation of colder clouds
embedded in the hot, rarefied medium is a well-known process appearing in many
astrophysical circumstances and environments. The characteristics of the
condensed clouds depend on the relevant timescales for cloud formation and
disruption due to either collisions or one of the operating instabilities. In
this paper, the importance of the Kelvin-Helmholtz instability is investigated
for the clouds forming in huge gaseous haloes of $L_\ast$ galaxies. Recent
treatment of this problem by Kamaya (1997) is extended and a more realistic
cooling function employed. Results show that the Kelvin-Helmholtz instability
proceeds effectively on the same timescale whether we account for self-gravity
or not. This has multiple significance, since these objects may have been seen
as high-column density absorption line systems against the background QSOs, and
probably represent the progenitors of the present-day globular clusters.
