  Polarisation observables are measured with the Crystal Barrel/TAPS experiment
at ELSA for photoproduction reactions with various final states, using a
circularly or linearly polarised photon beam and a longitudinally or
transversely polarised frozen spin butanol target. The Crystal Barrel/TAPS
setup provides a nearly 4$\pi$ angular coverage, a good energy resolution and a
high detection efficiency for photons, and is therefore ideally suited to study
final states comprising neutral mesons.
  Results for the measurement of the double polarisation observable E for pion
and eta photoproduction off the proton are presented.
