My last attendance at a meeting of the International Astronomical Union was forty-four years ago when it met in Paris in 1935. I do not doubt that my being asked to give an invited discourse at this meeting is a personal courtesy extended to me by your distinguished President recalling, perhaps, the years when he and I were colleagues together at the University of Chicago.

I am aware that associated with my absence from these meetings for nearly half a century is the fact that during most of this period - if not all of it - my interests, at different times, have been outside whatever may have been the prevailing trends in the mainstream of astronomy. I am afraid that on this account, the point of view I shall present - retrospectively and prospectively - will not be in conformity with the trends currently prevailing. I must therefore begin by asking for your patience and for your forbearance.

Dr. Blaauw, when he invited me to give one of the three discourses at this meeting, suggested that in selecting a topic I might wish to take into account the fact that this year is the centennial of Einstein’s birth. The subject of my discourse is in accordance with that suggestion.