  Cosmological theories for the origin and evolution of structure in the
Universe are highly predictive of the form of the angular power spectrum of
cosmic microwave background fluctuations. We present new results from a
comprehensive study of CMB observations which provide the first measurements of
the power spectrum all the way down to angular scales of ~10 arcminutes. On
large scales a joint likelihood analysis of the COBE and Tenerife data fixes
the power spectrum normalisation to be Q_rms = 21.0 +/- 1.6 uK for an initially
scale invariant spectrum of fluctuations. The combined data are consistent with
this hypothesis, placing a limit of n=1.3 +/- 0.3 on the spectral slope. On
intermediate scales we find clear evidence for a `Doppler' peak in the power
spectrum localised in both angular scale and amplitude. This first estimate of
the angular position of the peak is used to place a new direct limit on the
curvature of the Universe, corresponding to a density of
Omega=0.7^{+1.0}_{-0.4}. Very low density open Universe models are inconsistent
with this limit unless there is a significant contribution from a cosmological
constant.
