  The vertical scaleheight of the atomic hydrogen gas shows a remarkably flat
distribution with the galactocentric radius in the inner Galaxy. This has been
a long-standing puzzle (Oort 1962) because the gas scaleheight should increase
with radius when treated as responding to the gravitational potential of the
exponential stellar disk. We argue that the gravitational force of the
molecular and atomic hydrogen gas should also be brought into the picture to
explain this. We treat the stars, the HI and H_2 gas as three gravitationally
coupled components in the Galactic disk, and find the response of each
component to the joint potential and thus obtain their vertical distribution in
a self-consistent fashion. The effect of the joint potential is different for
the three components because of their different velocity dispersions. We show
that this approach cohesively and naturally explains the observed scaleheight
distribution of all the three components, namely, the HI and H_2 gas and the
stars, in the region studied (2-12 kpc). This includes the constant scaleheight
for the HI seen in the inner Galaxy. The effect of H_2 dominates in the
molecular ring region of 4-8.5 kpc, while that due to HI is dominant in the
outer Galaxy.
