Chapter One
THE DISCOVERY OF QUANTUM MECHANICS

I. INTRODUCTION
The laws of classical mechanics were summarized in 1686 by Isaac Newton (1642 1727) in his famous book Philosophiae Naturalis Principia Mathematica. During the following 200 years, they were universally used for the theoretical interpretation of all known phenomena in physics and astronomy. However, towards the end of the nineteenth century, new discoveries related to the electronic structure of atoms and molecules and to the nature of light could no longer be interpreted by means of the classical Newtonian laws of mechanics. It therefore became necessary to develop a new and different type of mechanics in order to explain these newly discovered phenomena. This new branch of theoretical physics became known as quantum mechanics or wave mechanics.
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