Contributions of Muslim scientists to optics

Sunday, 12 December 2010

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Written by Dr. Ragheb Elsergany

Introduction

Like many other sciences that appeared before Muslims, Greeks and ancient people were interested in optics and had their prints in the field that were used by Muslim scientists when practicing this science. They learnt from the Greeks about the refraction of light, burning mirrors etc. However, they did not only quote the Greeks but also added and expanded these principles and had their own inventions. They also managed to master this principle and that is why they went down in history.

Optics and Greek civilization

In the beginning, Greek optics had two conflicting opinions; the first is about intromission which sees vision as coming from something entering the eyes representative of the object and the second was emission, which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. The Greek civilization remained compromising these two different approaches and Aristotle’s efforts in this respect were lacking inevitable details. Euclid also had important efforts but his theories failed to accomplish fully explaining visual perception, because they ignored physics, physiological and psychological elements of visual phenomenon. He believed that that vision is caused by discrete rays which emanate from the eye and that things seen under a greater angle appear greater, and those under a lesser angle less. As for Ptolemy, despite his skill to compromise between engineering and physics handling of the issue, he finally failed. His handling of empirical results used to go side by side with previous deductions[1].  

Contributions of Muslim scientists to developing optics

Research in optics remained unchanged before the advent of the Islamic civilizations. Contributions by Muslim scientists had a unique and sophisticated pattern thanks to their excellence in related sciences such as astronomy, mechanical engineering, etc. Many of these sciences were used in their inventions.

Abu Yusuf Al-Kindi

Philsopher Abu Yusuf Al-Kindi[2] is one of the early Muslim scientists who studied physics and optics. He studied visual phenomenon and dealt with them in his famous book Kitab al-Manazir (Book of Optics). He used the Greek theory of emission. However, he added a detailed description of the principle of emission and then formulated a new conceptual system that finally replaced the theory of emission. His aforementioned book had a great influence in Arab scientific circles and later on in European circles during the Medieval[3].

Al-Hasan Ibn al-Haitham

He was followed by Al-Hasan Ibn al-Haitham, known to the West as Alhacen, whose scientific works made a breakthrough in optics and physiology of vision. His works were considered the basis on which Western scientists built all their theories in this principle. His works had a great influence on Western scientists- who raided them and attributed them to themselves- such as Roger Bacon and Witelo and others, especially in their researches related to the microscope, the telescope and the magnifying glass[4].

Ibn al-Haitham started first by discussing the theories of Euclid and Ptolemy in the field of vision and showed corruption of some of their aspects. During that time he presented a fine description of the eye, the eye lenses and eye vision. He described states of light ray refraction as it penetrates the air around the globe in general. Then he specifically described the state of light ray refraction when it penetrates a transparent body like air, water or molecules floating in the air. It bends – or refracts – off its course.

He researched in “reflection” and detection of the resulting angles. Ibn al-Haitham explained that celestial objects are seen at the horizon at sunrise before they are actually there. On the contrary, during sunset, the celestial objects continue to be seen at the horizon even after they hide below it. He is the first to suggest using the camera obscura (the black room) which is considered the basis of photography[5].

The book that immortalized the name of Ibn al-Haitham along the centuries is Kitab al-Manazir (Book of Optics). It clarifies the concept of optics as a primary theory in vision that is completely different than the assumption of visual rays that was preserved by mathematical tradition since Euclid and all the way to Al-Kindi. Ibn al-Haitham also added a new method to this explanation of the vision process. Thus he was able to rephrase concepts that were either meaningless (according to the visual ray theory) or ignored by philosophers who were more concerned with the explanation of nature of vision more than the actual process of vision[6].

Ibn al-Haitham wrote in optics about 24 books, including treaties, articles and books. However, most of these books were lost as part of our scientific heritage. Libraries in Istanbul and London and other capitals preserved some of these books. Kitab al-Manazir is a masterpiece work of Ibn al-Haitham. It contained innovative theories in optics, and remained the main reference in this science until the 17th century after being translated into Latin[7]. Kitab al-Manazir was a revolution in optics. In this book, Ibn al-Haitham did not adopt the theories of Ptolemy to explain and add only. Rather, he rebutted some of his theories in the science of light, reaching new theories that put the nucleus for modern optics.

Ptolemy, as we pointed out, claimed that vision happens when rays are emitted from the eyes and hit an object. Then following scientists adopted this theory. Then when Ibn al-Haitham came, he blew out this theory in his book “Kitab al-Manazir”. He showed that vision happens when rays are reflected off the object observed and into the eyes of the observer. This conclusion was reached after carrying out a set of experiments that showed that light rays travel in straight lines within a homogeneous medium and he proved this in his Kitab al-Manazir[8].  

Ibn al-Haitham also proved mathematically and geometrically how looking with both eyes at the same time at object happens without seeing a double vision. He explained that both images of the object are matched on the retina. Ibn al-Haitham placed with this proof and that explanation, the first foundation for what is known now as the steroscope.

Ibn al-Haitham was the first to study the eye scientifically and identified all its parts and anatomy and illustration. He was the first to give names to parts of the eye that the Westerns later took either with the same pronunciation or after translation. Some of these names are al-Qaraneyya (Cornea), al-Shabakeyya (Retina), as-Sa’el az-Zugagy (Vitrous Humour), and as-Sa’el al-Ma’ey (Aqueous Humour)[9].

He is the first to carry out experiments using the Hole Machine, or the Dark Room, or the camera obscura. This is how he discovered that the image appears upside down inside the room, then paved the way to inventing the camera. With this concept and these experiments, Ibn al-Haitham preceded the Italian scientists “Leonardo Da Vinci[10]” and “Della Porta” with five centuries[11].

Ibn al-Haitham placed for the first time the laws of refraction and deviation of optics. He explained how light refraction happens through mediums like water, glass and air. Thus he preceded the English scientist Newton.

He defined light in a similar manner to what we know today, and that it is a delicate body composed of rays with lengths and widths. He discussed its functions and defined refraction and specifically showed that the angle which with the light hits the object is exactly equal to the reflection angle in a mirror.

Ibn al-Haitham placed for the first time the laws of refraction and deviation. He explained how light refraction happens through mediums like water, glass and air. Thus he preceded the English scientist Newton[12].

One of his most notable accomplishments in his book “Kitab al-Manazir” was his previous experiment of the black box. It is considered the first step for inventing the camera. As the scientific encyclopaedia says, Ibn al-Haitham is considered the first inventor of cameras, and what is practically called Camera Obscura[13].

Anyone looks at Kitab al-Manazir by Ibn al-Haitham and its topics related to light immediately realizes that Ibn al-Haitham has his footprints in this principle. He authored this book in 411 A.H/1021 AD), capitalizing on his mathematical genius, scientific experiments and good experience to reach the top in this scientific field. He became one of the founders of sciences that changed scientists’ views about many things[14].

In spite of Ibn al-Haitham’s significance and his original researches in the field of optics, he remained unknown by a lot of people until Allah sent who would uncover his efforts and bring them to the light. Among those was the Arab scientist Moustafa Nazif who wrote a pioneer study about Ibn al-Haitham published by Cairo University in two volumes. He exerted a lot of effort to read Ibn al-Haitham’s manuscripts and hundreds of other references until he could clearly tell one evident fact; that Ibn al-Haitham put the basics of optics in its modern form at the beginning of the 11th century[15].

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