THE CLASSIFICATION OF CLUSTERS OF GALAXIES

of large spots and with concomitant long-duration Type IV radiation at radio frequencies. For other important Ha flares, especially those far from spots (e.g., 1959 July 14d14h45m), excellent X-sweep records have been secured, but give no evidence for the occurrence of "loops." Therefore, according to our records to date, the complex systems of loop-type prominences represent an even rarer solar phenomenon than do "important" Ha flares. 1 McMath, R. R., 0. C. Mohler, and H. W. Dodson, these PROCEEDINGS, 46, 165 (1960). 2 McMath, R. R., and E. Pettit, Astrophys. J., 85, 279 (1937) and 88, 244 (1938). 3 Sawyer, H. E., and J. Brodie, Pubis. Observatory Univ. Mich., 7, 79 (1938). 4 Ellison, M. A., S. M. P. McKenna, and J. H. Reid, Observatory, 80, 149 (1960).