Several methods have been proposed for calculating the magnitude and direction of the earth's magnetic field at locations above the earth's surface. During the 1962 Johnston Island explosions, observations were made of the man-made aurora caused by β particles guided into the southern conjugate region by the earth's magnetic field. The measured location of the initial disturbance was compared with the location calculated by several different models of the earth's magnetic field; the average differences between the observed and calculated points are tabulated. The Jensen and Cain coefficient set is found to give the smallest average difference in the region studied.