In addition to numerous emission lines arising from the ionization of chemical elements, well-exposed nebular spectrograms reveal a Balmer continuum in emission hitherto attributed to the second level radiative recombination of the hydrogen atoms and to the two-photon contribution. The very intense lines with regard to the adjacent continuous spectrum have been easily measured by many workers for identification, Balmer decrements, line ratios … whereas few data are available involving continuum measurements. As well as the mean slope of the continuum, the Balmer discontinuity is very sensitive to the physical conditions prevailing and the presence of dust in the nebulae.