  We report the first results from the BOOMERanG experiment, which mapped at
90, 150, 240 and 410 GHz a wide (3%) region of the microwave sky with minimal
local contamination. From the data of the best 150 GHz detector we find
evidence for a well defined peak in the power spectrum of temperature
fluctuations of the Cosmic Microwave Background, localized at $\ell = 197 \pm
6$, with an amplitude of $(68 \pm 8) \mu K_{CMB}$. The location, width and
amplitude of the peak is suggestive of acoustic oscillations in the primeval
plasma. In the framework of inflationary adiabatic cosmological models the
measured spectrum allows a Bayesian estimate of the curvature of the Universe
and of other cosmological parameters. With reasonable priors we find $\Omega =
(1.07 \pm 0.06)$ and $n_s = (1.00 \pm 0.08)$ (68%C.L.) in excellent agreement
with the expectations from the simplest inflationary theories. We also discuss
the limits on the density of baryons, of cold dark matter and on the
cosmological constant.
