This edition differs from the second chiefly in the addition of about
100 pages devoted to the quantum (or geometric, or Berry) phase, a
subject that did not exist when this book was written. The changes in
the remainder of the book consist of corrections of a small number of
misprints. While it may seem that adding two chapters on the quantum
phase is overemphasizing a currently fashionable subject, they actually
complete the development of quantum theory as given in this book. We
start with simple models, synthesizing them into complicated
"molecules." With the new chap- ters. we end with complicated
"molecules," dividing them into simpler parts. This process of dividing
a complex system into parts quite naturally gives rise to a gauge
theory, of which the geometric phase is a manifestation - with
consequences not only in theory, but observable in experiments. For this
rea- son, the geometric phase is not a mere fashion, but a discovery
that will retain its importance forever and must be discussed in
textbooks on quantum mechanics. to acknowledge help and advice from Mark
Loewe with the I would like writing and also of the new part of the
book. In addition, I would like to express my gratitude to J. Anandan,
M. Berry, and c.A. Mead, who have read parts or all of the new material
and have provided valuable advice.