A study of the arrival direction distribution of high-energy particles as observed from the Northern Hemisphere

Measurements are reported on the arrival direction distribution of over 70000 carefully selected showers with energies above 6*10 16 eV detected at Haverah Park since 1963. After showing that spurious effects do not significantly perturb the data the authors find that the probability of isotropy in the energy region 6*10 16 eV to 10 20 eV is less than 3% and that there is evidence to suggest that the arrival directions are complex functions of energy and declination. There is a significant anisotropy of about 2% in the first harmonic of right ascension in the direction 251 degrees for energies near 10 17 eV, and a significant 6% first harmonic in the direction 46 degrees RA for energies near 10 18 eV. Some of the particles of highest energy arrive nearly perpendicular to the Galactic Plane.