  We investigate the thermodynamics of a Bose gas interacting with repulsive
forces and confined in a harmonic trap. We show that the relevant parameters of
the system (temperature, number N of atoms, harmonic oscillator length,
deformation of the trap, s-wave scattering length) fix its large N
thermodynamic behaviour through two dimensionless scaling parameters. These are
the reduced temperature t=T/T^0_c and the ratio \eta between the T=0 value of
the chemical potential, evaluated in the Thomas-Fermi limit, and the critical
temperature T_c^0 of the non-interacting model. The scaling functions relative
to the condensate fraction, energy, chemical potential and moment of inertia
are calculated within the Popov approximation.
