I wish to acknowledge the many general sources of information which provided standard definitions and descriptions of the various physical phenomena related to the nature of time.

In addition, I have referred to specific sources which include information on commonly defined time scales and standards, among them government publications and scientific perspectives, as well as specialized accounts by physicists, astronomers, geologists, biologists, psychologists, anthropologists, and others.

I am especially indebted to my wife, Mary Briggs, for enduring the many conversations on the nature of time, and to Donald Burgy and Ron Wallace for their critical support of the text.

The text was first presented in its spoken version in Boston in 1990, and was revised and presented again in 1995. The second edition was published in 1995.

– J. H.