  We report the first detection of the Sunyaev-Zel'dovich increment on the
cosmic microwave background (CMB) at submillimetre wavelengths in the direction
of a cluster of galaxies.It was achieved towards the rich cluster Abell 2163,
using the PRONAOS 2-metre stratospheric telescope. Together with data from the
SuZIE, Diabolo, and ISO-PHT experiments, these measurements, for the first
time, give a complete picture of the far-infrared to millimetre spectral energy
distribution of the diffuse emission toward a cluster of galaxies. It clearly
shows the positive and negative parts of the S.Z. effect and also a positive
signal at short wavelengths that can be attributed to foreground dust in our
galaxy.
