A search for fine structure of the knee in EAS size spectra

Twenty eight size spectra of extensive air showers in the knee region from seven different experiment are analysed consistently. They are fitted by adjusting either four or five parameters: knee position, power law exponents above and below the knee region, 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 five parameters are employed no systematic deviation from a simple smooth knee is apparent at the 1% level up to about 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.