Challenges and prospects for better measurements of the CMB intensity
  spectrum
  Spectral distortions of the Cosmic Microwave Background (CMB) offer the
possibility of probing processes which occurred during the evolution of our
Universe going back up to Z$\simeq 10^7$. Unfortunately all the attempts so far
carried out for detecting distortions failed. All of them were based on
comparisons among absolute measurements of the CMB temperature at different
frequencies. We suggest a different approach: measurements of the frequency
derivative of the CMB temperature over large frequency intervals instead of
observations of the absolute temperature at few, well separated, frequencies as
frequently done in the past, and, direct measurements of the foregrounds which
hinder bobservations, at the same site and with the same radiometer prepared
for the search of CMB distortions. We discuss therefore the perspectives of new
observations in the next years from the ground, at very special sites, or in
space as independent missions or part of other CMB projects
