  We determine the physical conditions in NGC 6543, obtaining two different
estimates of the electron temperature (T_e) and one estimate of the electron
density (N_e). The electron temperature is computed by means of the [O III]
ratio lambda 5007/lambda 4363, and of the diagnostic diagram combining lambda
5007 to the [O III] infrared lines 52m and 88m. The continuum intensity
measured on slit spectra is much higher than theoretically predicted under the
simplest assumptions. After considering several possibilities, we suggest
enhanced 2-photon emission as the most probable source of the additional
continuum. While T_e and N_e derived from the diagnostic diagram agree with the
most recent determination, T_e derived from lambda 5007/lambda 4363 is smaller
than previously published values, probably due to the bias in lambda 4363
introduced by the uncertainty in the continuum. Our main conclusion is that it
is not possible, with present-day data, to derive accurate temperature maps of
photoionized nebulae.
