The size-line width relation and the size-density relation are analyse
d for the molecular clouds from the CfA 1.2m telescope CO survey at hi
gh latitudes in the second quadrant. It is found that Delta v proporti
onal to r(0.5) and n proportional to r(-0.8), with correlation coeffic
ient r = 0.66 and r = -0.86, respectively It is also shown that the vi
rial mass is correlated to the CO luminosity, log(M(vir)) = (0.78 +/-
0.09)log(L(CO)) + (2.3 +/- 0.1). The size, line width, and radius for
high latitude molecular clouds thus follow similar relations as found
for giant molecular clouds. For the latter clouds these relations are
usually interpreted as a consequence of virial equilibrium for clouds
which are gravitational bound. It is shown that this interpretation is
not valid for high latitude molecular clouds. The volume filling fact
or of molecular gas in high-latitude clouds is found to be rather low,
less than 0.01. The pressure induced on the clouds by the surrounding
HI gas is larger than the internal pressure induced by the motion of
the molecular gas, indicating that the clouds are compressed by the ex
ternal HI gas.