28 size spectra of extensive air showers from 7 different experiments are
analysed consistently. They are fitted by adjusting either 4 or 5 parameters:
knee position, power law exponents above and below the knee, overall intensity
and, in addition, a parameter describing the smoothness of the bend. The
residuals are then normalized to the same knee position and averaged. When 5
parameters are employed no systematic deviation from a single smooth knee is
apparent at the 1% level up to a factor of 4 above the knee. At larger shower
sizes a moderately significant deviation can be seen whose shape and position
are compatible with a second knee caused by iron group nuclei.Comment: 17 pages, 5 figs.; Astroparticle Physics, in pres
