Search for a Sidereal Variation of the Cosmic Ray Intensity at High Energies

Extensive air showers with energies of about 10 16 eV and 10 17 eV have been recorded at geographic latitude 53° N by means of counter sets separated by about 150 m and 300 m. Harmonic analysis of the shower frequencies has revealed no evidence for a sidereal daily variation with amplitude exceeding the statistical uncertainties, which are 2.5% and 6% respectively. No evidence has been found for a solar daily variation with amplitude exceeding 2.5% for 10 16 eV showers. A solar daily variation has been found for 10 17 eV showers with an amplitude of 19% and a time of maximum at about 1300 h. The interpretation of this result is briefly discussed.