Galactic magnetic field irregularities and their effect on cosmic ray propagation at energies above 1017eV

Astronomical data have been examined with regard to the characteristics of the irregular component of the magnetic field in the galaxy. A model has been formulated for the irregular field, and cosmic ray trajectories have been traced through the aggregate field. Comparison of experimental data on the arrival directions of extensive air showers with the predicted distributions shows that if the primary cosmic rays are protons then the majority between about 7*10 17 eV and 10 19 eV must be of extragalactic origin. Outside these limits the present arrival direction data do not allow distinction to be drawn between galactic and extragalactic origin.