Undoubtedly, nearly all who read this book have, at one time or another, pondered the question, "What is light?" To answer, "Light is that which permits vision," begs the question, for such an answer provides us with no understanding of the nature of light. It says no more that "light is light."
Describing the nature of light has been bothersome for countless years. This is attributable to a variety of facts. Most important, light is a subtle matter that is perceived by imperfectly understood sensors. (Does the light reflected from this page induce a perception that is markedly different from the sensation achieved in a dream?)Light is also manifest in an exceedingly broad range of circumstances. Light is emitted from hot bodies, from lightning discharges, from some insects, and from some not well-defined processes. Light is all about us, stimulating our most perceptive sense - vision.
Light is also of great aesthetic value. The poet, William Wordsworth, wrote, "My heart leaps up when I behold/A rainbow in the sky." This thought is reflected in the emotion occasioned in the minds of countless men from the dawn of antiquity. A study of the rainbow evokes added joy to its perception. Such a study entails gaining some knowledge of the nature of light.
From this deeper appreciation of the rainbow we are led to study such fascinating phenomena as halos, mirages, and phantasmagoria. Simpler things, too, command our attention: the blue of the sky, the red of the setting sun, the whiteness of clouds, blue shadows on snow-covered fields, and the colors of flowers and birds. Light is certainly fundamental in much of our aesthetic pleasure. Apart from these pleasures, we study the nature of light because of its role in technology. The telescope and microscope, photography, lasers, optical fibers, and many other devices are based upon a knowledge of the nature of light.
No wonder, then, that man asks, "What is light?" We frequently resort to operational definitions in an attempt to answer that question. That is, when we confront such phenomena as the photoelectric effect we conceive of light as a bombardment of miniature bullets, or corpuscles. On the other hand, light is evident by such phenomena as diffraction, polarization, and interference. This leads us to conceive of light as causing a wave disturbance. This dichotomy was resolved by quantum mechanics from which these macro-analogies were replaced with a conception of light existing in atomic dimensions with sufficient momentum to interact with matter and produce the photoelectric effect, but guided through space by an electromagnetic wave.
The history of man's investigations of the nature of light is fascinating. It encompasses a large cast of characters who interact with all facets of the history of mankind. The anecdotes presented here describe a few of the events which took place in man's search for the nature of light - a search which included drama, adventure, humor, political and religious entanglements, pestilence, and the many foibles of men. Some of the men involved displayed enormous conceit; others were humble. Some were born to wealth; others had to overcome poverty.
I will consider my task accomplished if some who read this are motivated to a greater joy in observing nature's splendors and to extend themselves to further investigations of the nature of light. You must not, however, consider these anecdotes to be more than stories informing you of some of the incidents in the lives of the men who made significant contributions to optics. This book is neither a history nor an optics text.
The material used in preparing these anecdotes was derived from various sources. The books which dominated the search are listed in the bibliography. In addition, journal articles have proved to be an invaluable source of information. Most joyful of all the sources, undoubtedly, were visits to museums. Those in Europe are of particular value for historical research. Not the least of my sources has been numerous personal interviews. Because my sources are so diverse, I have refrained from citing references. To do so would obscure the text and, in any event, it would be of marginal benefit to the reader if I were to cite discussions or visits. Naturally, I shall be pleased to assist anyone desiring to locate specific source material.
A few of the anecdotes have been published in approximately their present form in Optical Engineering and ISIS. The anecdotes constitute distinct stories that need not be read in order. Some attempt has been made to arrange them chronologically but, as this is not intended to be an historical account, the arrangement is not considered of importance.
To cite my appreciation to all who have contributed to this effort would require several pages. Suffice it to say that I have considerable help for which I am very grateful.
I've enjoyed preparing these anecdotes; I hope that you enjoy reading them.
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