The writer is deeply indebted to many persons for various reasons concerning the present paper:
To Helmut Abt, for making the investigation possible by offering a large number of spectrograms obtained by him at Kitt Peak National Observatory. He has also given valuable suggestions in the course of this work.
To Dimitri Mihalas, for many discussions through the years on problems connected with one of his fields of highest distinction, stellar atmospheres, and for his continuing encouragement of the writer's attempts to explore certain conceptual fields.
To Lewis Hobbs and Al Harper, in their successive periods of Directorship of the Yerkes Observatory, for their support of the writer's efforts to continue creative research; to the University of Chicago for its encouragement of this work.
To Robert Garrison for arranging and hosting the June 1983 conference at the University of Toronto, where the present paper was given.
To Don Osterbrock of the Lick Observatory, for his continued encouragement during the course of this work.
To Richard Kron for discussions of problems.
To Paul Rybski for numerous conversations concerning fundamental issues raised in connection with this paper.
To Richard D. Dreiser for preparing the three illustrations.
To Mrs. E. Cox and Mrs. J. Draeger for stenographic help.