  We report on the realization of a trapped one dimensional Bose gas and its
characterization by means of measuring its lowest lying collective excitations.
The quantum degenerate Bose gas is prepared in a 2D optical lattice and we find
the ratio of the frequencies of the lowest compressional (breathing) mode and
the dipole mode to be $(\omega_B/\omega_D)^2\simeq3.1$, in accordance with the
Lieb-Liniger and mean-field theory. For a thermal gas we measure
$(\omega_B/\omega_D)^2\simeq4$. By heating the quantum degenerate gas we have
studied the transition between the two regimes. For the lowest number of
particles attainable in the experiment the kinetic energy of the system is
similar to the interaction energy and we enter the strongly interacting regime.
