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What is light, really? Christiaan Huygens, one of the smartest men of the 1600s, said light moves in waves, like ripples spreading on water. In this book he explains mirrors, bending light, and a strange crystal from Iceland that splits one ray into two. His reasoning is careful and step by step, drawn from experiments anyone can picture. Newton argued differently later, but Huygens started a debate that made science better.
Christiaan Huygens, the Dutch mathematician and astronomer who discovered the rings of Saturn and built the first practical pendulum clock, presented his theory of light to the Paris Academy in 1678. He published it in 1690, and it appears here in Silvanus Thompson's English translation. It is one of the founding documents of physical optics, short enough to read entire and clear enough to follow with attention.
Huygens proposes that light travels as waves spreading through an invisible ether, each point of a wave front becoming the source of new wavelets. From that single idea he derives the laws of reflection and refraction with beautiful economy, and then tackles the strange double refraction of Iceland spar, a crystal that splits one ray into two. His demonstrations lean on geometrical figures throughout, so keep a pencil nearby and sketch as you read.
Newton's particle theory eclipsed the wave view for a century, but Huygens was largely right, and his principle still bears his name in textbooks. Readers who like watching a great idea do hard work, elegantly and with few tools, will prize this treatise.
Christiaan Huygens, the Dutch astronomer and physicist who ground his own lenses and discovered Saturn's rings, presented his Treatise on Light in 1690, here in Silvanus P. Thompson's translation. He argues that light travels as waves through an ether, and uses that idea to explain reflection, refraction, and the strange double refraction of Iceland crystal. It offers a founding text of wave optics, elegant and exact.
Huygens wrote this treatise in France and read it to the Royal Academy of Sciences in Paris in 1678; it was published in 1690, and it presents the first fully worked out wave theory of light. This is Silvanus P. Thompson's translation, carried here with Huygens's preface and the translator's note.
Six chapters do the work. Huygens begins with rays propagated in straight lines, then takes up reflexion and refraction, the refraction of the air, and the strange refraction of Iceland crystal, the double refraction that his wave construction explains with particular elegance, before closing on the figures of transparent bodies. At the center stands the principle that still bears his name: every point on a wave front becomes the source of a new wave, and the envelope of those waves is the light's next position.
The demonstrations refer constantly to geometrical figures, which plain text cannot carry, so a reader should expect to sketch or imagine the diagrams. The reasoning itself is complete and remarkably modern. Newton published the rival corpuscular account fourteen years later; this is the other side of that great argument, stated by its author.
Edition: Translated by Silvanus P. Thompson. Text: Project Gutenberg ebook 14725.
The first chapter
Considering the great influence which this Treatise has exercised in the development of the Science of Optics, it seems strange that two centuries should have passed before an English edition of the work appeared. Perhaps the circumstance is due to the mistaken zeal with which formerly everything that conflicted with the cherished ideas of Newton was denounced by his followers. The Treatise on Light of Huygens has, however, withstood the test of time: and even now the exquisite skill with which he applied his conception of the propagation of waves of light to unravel the intricacies of the phenomena of the double refraction of crystals, and of the refraction of the atmosphere, will excite the admiration of the student of Optics. It is true that his wave theory was far from the complete doctrine as subsequently developed by Thomas Young and Augustin Fresnel, and belonged rather to geometrical than to physical Optics. If Huygens had no conception of transverse vibrations, of the principle of interference, or of the existence of the ordered sequence of waves in trains, he nevertheless attained to a remarkably clear understanding of the principles of wave-propagation; and his exposition of the subject marks an epoch in the treatment of Optical problems. It has been needful in preparing this translation to exercise care lest one should import into the author's text ideas of subsequent date, by using words that have come to imply modern conceptions. Hence the adoption of as literal a rendering as possible. A few of the author's terms need explanation. He uses the word "refraction," for example, both for the phenomenon or process usually so denoted, and for the result of that process: thus the refracted ray he habitually terms "the refraction" of the incident ray. When a wave-front, or, as he terms it, a "wave," has passed from some initial position to a subsequent one, he terms the wave-front in its subsequent position "the continuation" of the wave. He also speaks of the envelope of a set of elementary waves, formed by coalescence of those elementary wave-fronts, as "the termination" of the wave; and the elementary wave-fronts he terms "particular" waves. Owing to the circumstance that the French word rayon possesses the double signification of ray of light and radius of a circle, he avoids its use in the latter sense and speaks always of the semi-diameter, not of the radius. His speculations as to the ether, his suggestive views of the structure of crystalline bodies, and his explanation of opacity, slight as they are, will possibly surprise the reader by their seeming modernness. And none can read his investigation of the phenomena found in Iceland spar without marvelling at his insight and sagacity.
S.P.T.
June, 1912.
Source: Project Gutenberg. Published 1690. Author died 1695. Silvanus P. Thompson translation. Public domain worldwide. Share this book: WhatsApp
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