  The Dual Imaging Cerenkov Experiment (DICE) was designed and operated for
making elemental composition measurements of cosmic rays near the knee of the
spectrum at several PeV. Here we present the first results using this
experiment from the measurement of the average location of the depth of shower
maximum, <X_max>, in the atmosphere as a function of particle energy. The value
of <X_max> near the instrument threshold of ~0.1 PeV is consistent with
expectations from previous direct measurements. At higher energies there is
little change in composition up to ~5 PeV. Above this energy <X_max> is deeper
than expected for a constant elemental composition implying the overall
elemental composition is becoming lighter above the knee region. These results
disagree with the idea that cosmic rays should become on average heavier above
the knee. Instead they suggest a transition to a qualitatively different
population of particles above 5 PeV.
