Includes bibliographies.

Introduction to Einstein’s theory of relativity (1921).--Physical aspects of quantum mechanics.--On the meaning of physical theories.--Cause, purpose, and economy in natural laws.--Einstein’s statistical theories.--Physics in the last fifty years.--Is classical mechanics in fact deterministic?--Astronomical recollections.--Statistical interpretation of quantum mechanics.--Physics and relativity.--Development and essence of the atomic age.--A New Year’s message.--Symbol and reality.--What is left to hope for?--In memory of Einstein.--From the postscript to the Restless Universe (1951)

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