Book of Optics

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The Book of Optics (Arabic: Kitab al-Manazir, Latin: De Aspectibus) was a seven volume treatise on optics, physics, anatomy, mathematics and psychology written by the Iraqi Arab Muslim scientist Ibn al-Haytham (Latinized as Alhacen or Alhazen in Europe) from 1011 to 1021, when he was under house arrest in Cairo, Egypt. The book had an important influence on the development of optics, and science in general, as it drastically transformed the understanding of light and vision, and introduced the experimental scientific method. As a result, Ibn al-Haytham has been described as the "father of optics", the "pioneer of the modern scientific method", and the "first scientist". The Book of Optics has been ranked alongside Isaac Newton's Philosophiae Naturalis Principia Mathematica as one of the most influential books in the history of physics, for initiating a scientific revolution in optics and visual perception.

The Book of Optics also contains the earliest discussions and descriptions of the psychology of visual perception and optical illusions, as well as experimental psychology, and the earliest descriptions of the camera obscura, a precursor to the modern camera. In medicine and ophthalmology, the book also made important advances in eye surgery, as it correctly explained the process of sight for the first time. The work also had an influence on the use of optical aids in Renaissance art and the development of the telescope and microscope.

Overview

Optics and vision

In classical antiquity, there were two major theories on vision. The first theory, the emission theory, was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light. The second theory, the intromission theory, supported by Aristotle and his followers, had physical forms entering the eye from an object. Alhacen argued on the basis of common observations (such as the eye being dazzled or even injured if we look at a very bright light) and logical arguments (such as how a ray could proceeding from the eyes reach the distant stars the instant after we open our eye) to maintain that we cannot see by rays being emitted from the eye nor through physical forms entering the eye. Alhacen instead developed a highly successful theory which explained the process of vision by rays of light proceeding to the eye from each point on an object, which he proved through the use of experimentation.

Ibn al-Haytham proved that rays of light travel in straight lines, and carried out a number of experiments with lenses, mirrors, refraction, and reflection. He was also the first to reduce reflected and refracted light rays into vertical and horizontal components, which was a fundamental development in geometric optics. He also discovered a result similar to Snell's law of sines, but did not quantify it and derive the law mathematically. Ibn al-Haytham is also credited with the invention of the camera obscura and pinhole camera. Alhacen also wrote on the refraction of light, especially on atmospheric refraction, for example, the cause of morning and evening twilight. He solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. He also experimented on the dispersion of light into its constituent colours, speculated on the finite speed, rectilinear propagation and electromagnetic aspects of light, and argued that rays of light are streams of tiny particles travelling in straight lines.

Ibn al-Haytham made a thorough examination of the passage of light through various media and discovered the laws of refraction. He also carried out the first experiments on the dispersion of light into its constituent colours. His book Kitab al-Manazir (Book of Optics) was translated into Latin in the Middle Ages, as also was his book dealing with the colours of sunset. He dealt at length with the theory of various physical phenomena such as shadows, eclipses, and the rainbow, and speculated on the physical nature of light. He is the first to describe accurately the various parts of the eye and give a scientific explanation of the process of vision. He also attempted to explain binocular vision and the apparent increase in size of the Sun and the Moon when near the horizon. He is known for the earliest use of the camera obscura. He contradicted Ptolemy's and Euclid's theory of vision that objects are seen by rays of light emanating from the eyes; according to him the rays originate in the object of vision and not in the eye. Through these extensive researches on optics, he has been considered as the father of modern optics.

In his work on optics, Alhacen described sight as the inference of distinct properties of two similar and dissimilar objects. The eye perceives the size, shape, transparency (color and light), position, and motion from cognitive distinction which is entirely different from perceiving by mere sensation the characteristics of the object. The faculty of the mind, for Alhacen, includes perceiving through judgement and inference of distinct properties of similar objects outline and structure. Alhacen continues this body of work by concluding that the discrimination performed by the faculty of judgment and inference is in addition to sensing the objects visible form and not by pure sensation alone. We recognize visible objects that we frequently see. Recognition of an object is not pure sensation because we do not recognize everything we see. Ultimately, recognition does not take place without remembering. Recognition is due to the inference because of our mental capacity to conclude what objects are. Alhacen uses our ability to recognize species and likening their characteristics to that of similar individuals to support recognition associated and processed by inference. Alhacen further concludes that we are processing visual stimuli in very short intervals which allows us to recognize and associate objects through inference but we do not need syllogism to recognize it. These premises are stored infinitely in our souls.

Sami Hamarneh writes several examples of Ibn al-Haytham's descriptions which are correct according to modern optics:

"He explained that sight results from the light penetrating the eye from the object, thus initiating a revolt against the ancient belief that visionary rays emanate from the eye."
"He showed that the corneal region of the eye is curved and is close to the conjunctiva; but the cornea do not coalesce with the conjunctiva."
"He suggested that the inner surface of the cornea at the point where it joins the foramen of the eye becomes Concave in accordance with the curvature of its outer surface. The edges of the surfaces of the foramen and the middle part of the corneal regions become even but not one."
"He endeavored by use of hyperbola and geometric optics to chart and formulate basic laws on reflection, and on atmospheric and light-ray refraction. He speculated on electromagnetic aspects of light, its velocity, and its rectilinear propagation. He recorded formation of an image in a camera obscura during an eclipse of the sun (the principle of the pinhole camera)."
"He stated that the lens is that part of the eye where vision is felt first."
"He theorized on how the image is transmitted through the optic nerve to the brain and made a distinction between luminous and nonluminous bodies."

The Book of Optics is considered by some to mark the beginning of experimental psychology. Ibn al-Haytham made use of his experimental method in his pioneering work on the psychology of visual perception and optical illusions. While his investigations and experiments on psychology and visual perception included sensation, variations in sensitivity, sensation of touch, perception of colours, perception of darkness, the psychological explanation of the moon illusion, and binocular vision.

Other apparatus Ibn al-Haytham described in the Book of Optics, besides the camera obscura, include "specially arranged dark chambers, specially designed apertures for the controlled admission of light," and "viewing tubes".

Scientific method

Roshdi Rashed notes that "by promoting the use of experiments in scientific research, al-Haytham played an important part in setting the scene for modern science. Rosanna Gorini wrote the following on the Book of Optic's introduction of the scientific method:

Ibn al-Haytham's scientific method was very similar to the modern scientific method and consisted of the following procedures:

Observation
Statement of problem
Formulation of hypothesis
Testing of hypothesis using experimentation
Analysis of experimental results
Interpretation of data and formulation of conclusion
Publication of findings

From Ibn al-Haytham to the present day, the emphasis of the scientific method has always been on seeking truth:

The conjecture that "Light travels through transparent bodies in straight lines only", was corroborated by Alhacen only after years of effort. His demonstration of the conjecture was to place a straight stick or a taut thread next to the light beam, to prove that light travels in a straight line.

The term "experiment" itself may have origins in the Book of Optics. Ibn al-Haytham used the Arabic terms i'tabara, 'itibar and mu'tabir to refer to his experiments. During the Latin translation of the book, these terms were rendered into Latin as experimentare (or experiri), experimentum and experimentatar respecively.

Legacy

Robert S. Elliot wrote the following on the Book of Optics:

George Sarton, the father of the history of science, wrote in the Introduction to the History of Science:

Latin translations

Optics was translated into Latin by an unknown scholar at the end of the 12th century or the beginning of the 13th century. It was printed by Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus

Risner is also the author of the name variant "Alhazen", before him he was known in the west as Alhacen, which is correct transcription of the Arabic name. This work enjoyed a great reputation during the Middle Ages. Works by Alhacen on geometrical subjects were discovered in the Bibliothèque nationale in Paris in 1834 by E. A. Sedillot. Other manuscripts are preserved in the Bodleian Library at Oxford and in the library of Leiden. Ibn al-Haytham's optical studies were influential in a number of later developments, such as the telescope, which laid the foundations of telescopic astronomy.

Volumes

Book I

In Book I of the treatise, Ibn al-Haytham begins by writing an introduction to the systematic approach he will use for his investigations on optics, and correctly explains how vision is perceived by rays of light travelling in straight lines from an object to the eye:

He also states that his investigation of light will be based on experimental evidence rather than on abstract theory, and notes that light is always the same from every source, using sunlight, fire, and a mirror as examples. He then examines the anatomical structure of the eye, and proposes the first use of a camera obscura.

Books II–III

Book II of the treatise contains a discussion on visual perception. In Book III, he pioneered the psychology of visual perception and optical illusions, being the first scientist to argue that vision occurs in the brain, rather than the eyes. He pointed out that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. He explained possible errors in vision in detail, and as an example, describes how a small child with less experience may have more difficulty interpreting what he/she sees. He also gives an example of an adult that can make mistakes in vision because of how one's experience suggests that he/she is seeing one thing, when he/she is really seeing something else.

Books IV–VII

Book IV deals with the theory of reflection mathematically, while Book V deals with the influential Alhazen's problem. Book VI examines errors in vision due to reflection, while the final volume, Book VII, examines refraction.

Treatise on Light

Ibn al-Haytham's Risala fi l-Daw’ (Treatise on Light) is a supplement to his Kitab al-Manazir (Book of Optics). The text contained further investigations on the properties of luminance and its radiant dispersion through various transparent and translucent media. He also carried out further observations, investigations and examinations on the anatomy of the eye, the camera obscura and pinhole camera, the illusions in visual perception, the meteorology of the rainbow and the density of the atmosphere, various celestial phenomena (including the eclipse, twilight, and moonlight), refraction, catoptrics, dioptrics, spherical and parabolic mirrors, and magnifying lenses.

According to Giambattista della Porta, Ibn al-Haytham was the first to give a correct explanation of the apparent increase in the size of the Moon and Sun when near Earth's horizon, known as the Sun and Moon illusion respectively. (Ptolemy made earlier attempts at explaining it, according to Roger Bacon.)

Other contributions

While the Book of Optics was mainly concerned with the field of optics, the book also had a significant influence on several other fields of science, mathematics and philosophy.

Alhazen's problem

Ibn al-Haytham's work on catoptrics in Book V of the Book of Optics contains the important mathematical problem known as Alhazen's problem. It comprises drawing lines from two points in the plane of a circle meeting at a point on the circumference and making equal angles with the normal at that point. This leads to an equation of the fourth degree. This eventually led Ibn al-Haytham to derive the earliest formula for the sum of the fourth powers, and using an early proof by mathematical induction, he developed a method for determining the general formula for the sum of any integral powers, which was fundamental to the development of infinitesimal and integral calculus.

Ibn al-Haytham solved the problem using conic sections and a geometric proof, but Alhazen's problem remained influential in Europe, when later mathematicians such as Christiaan Huygens, James Gregory, Guillaume de l'Hôpital, Isaac Barrow, and many others, attempted to find an algebraic solution to the problem, using various methods, including analytic methods of geometry and derivation by complex numbers. Mathematicians were not able to find an algebraic solution to the problem until the end of the 20th century.

Astronomy

Chapters 15-16 of the Book of Optics dealt with astronomy. Ibn al-Haytham was the first to discover that the celestial spheres do not consist of solid matter, and he also discovered that the heavens are less dense than the air:

These views were later repeated by Witelo and had a significant influence on the Copernican and Tychonic systems of astronomy.

Biomedical sciences

Ibn al-Haytham discussed the topics of medicine, ophthalmology and eye surgery in the anatomical and physiological portions of the Book of Optics and in his commentaries on Galenic works. He made several improvements to eye surgery and accurately described the process of sight, the structure of the eye, image formation in the eye and the visual system. He also discovered the underlying principles of Hering's law of equal innervation, binocular vision, motion perception, vertical horopters, and binocular disparity.

Regarding the process of image formation, he incorrectly agreed with Avicenna that the lens was the receptive organ of sight, but hinted at the retina also being involved in the process.

Hockney-Falco thesis

At a scientific conference in February 2007, Charles M. Falco argued that Ibn al-Haytham's work on optics may have influenced the use of optical aids by Renaissance artists. Falco said that his and David Hockney's examples of Renaissance art "demonstrate a continuum in the use of optics by artists from circa 1430, arguably initiated as a result of Ibn al-Haytham's influence, until today.

His principle of linear perspective was also employed in the art of Leonardo da Vinci and other Renaissance artists.

Phenomenology

In philosophy, Ibn al-Haytham is considered a pioneer of phenomenology. He articulated a relationship between the physical and observable world and that of intuition, psychology and mental functions. His theories regarding knowledge and perception, linking the domains of science and religion, led to a philosophy of existence based on the direct observation of reality from the observer's point of view. Much of his thought on phenomenology was not further developed until the 20th century.

Psychology

Ibn al-Haytham is considered by some to be the founder of experimental psychology, for his pioneering work on the psychology of visual perception and optical illusions. Ibn al-Haytham made many subjective reports regarding vision and can therefore be argued to be the first "psychologist".

In the Book of Optics, Ibn al-Haytham was the first scientist to argue that vision occurs in the brain, rather than the eyes. He pointed out that personal experience has an effect on what people see and how they see, and that vision and perception are subjective. He explained possible errors in vision in detail, and as an example described how a small child with less experience may have more difficulty interpreting what he or she sees. He also gave an example of how an adult can make mistakes in vision due to experience that suggests that one is seeing one thing, when one is really seeing something else.

In the Book of Optics, Ibn al-Haytham also developed the "concept of a sensory core that interprets visual stimuli" and which was "highly sophisticated, incorporating mathematical, anatomical and physiopsychological components."

Ibn al-Haytham also described what became known as Hering's law of equal innervation, vertical horopters, and binocular disparity, and improved on the theories of binocular vision, motion perception and horopters previously discussed by earlier scholars such as Aristotle, Euclid and Ptolemy.

Omar Khaleefa has argued that Ibn al-Haytham should be considered the founder of psychophysics, contrary to the orthodox opinion that Gustav Fechner founded this field in 1860 with the publication of his Elements of Psychophysics. There is, however, no evidence that Ibn al-Haytham employed any quantitative psychophysical techniques, so this remains a minority opinion.

Theology

Ibn al-Haytham attributed his experimental scientific method and scientific skepticism to his Islamic faith. He believed that human beings are inherently flawed and that only God is perfect. He reasoned that to discover the truth about nature, it is necessary to eliminate human opinion and error, and allow the universe to speak for itself.

Ibn al-Haytham described his search for truth and knowledge as a way of leading him closer to God:

References

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