The Book of Optics
November 18, 2007
Somewhere between 965 -1039 lived Ibn Al-Haytham (Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham) a visionary. He is known for his theories on visual perception and Optics. More about Al-Haytham here…
Read the english translation of Kitab al Manazir – The book of Optics, here.
You may also visit this page by Bradley Steffens. He is the author of the book Ibn Al-Haytham – First Scientist.
November 19, 2007 at 7:36 pm
I am glad to see you are bringing attention to Ibn al-Haytham’s contributions. I am the author of Ibn al-Haytham: First Scientist, the world’s first full biography of the great eleventh-century scholar who not only contributed to the field of optics, but was the first person to insist on systematically testing hypotheses with experiments, earning himself a place in history as the first scientist. I hope you will consider including my book in your MyBooks at GoogleBooks.
November 29, 2007 at 1:21 am
I am preparing a History of Science course at my college and I found the translation of Ibn Al-Haytham’s theory of perception very enlightening. I have been looking for, but cannot find, a description of the experiments he did with the camera obscura. I have found summaries and things such as “He performed many experiments …”, but no real description that includes his use of what is now known as the scientific method. Is this also contained with in the “Book of Optics”? If not, where might I find this? I would like to use this experiment in the course.
November 30, 2007 at 6:26 am
Ibn al-Haytham did perform many experiments with light, but only one that includes a complete description of the camera obscura. A similar experiment, designed to test if light emanates from each part of a candle and moves in straight lines, also uses a source of illumination projected onto a screen, but the light travels through a long, thin tube that protrudes through a copper sheet. The projected image is of a very small part of the candle flame.
I discuss the more complete camera obscura experiment in my book, Ibn al-Haytham: First Scientist, on pages 68-70. I quote from Ibn al-Haytham, The Optics of Ibn al-Haytham, tr. A.I. Sabra. London: The Warburg Institute, 1989, vol. I, p. 90-91. In my book, I mix quotations from the book with my own explanations. Here is how the entire experiment reads in Dr. Sabra’s translation:
The proof that lights and colours do not blend in the air or in transparent bodies is [the following]. Let several lamps be positioned at various points in the same area, all being opposite a single aperture leading to a dark place; opposite the aperture let there be a wall in that dark place or let an opaque body be held facing the aperture: the lights of those lamps will appear separately on that wall or body and in the same number as the lamps, each light being opposite one of the lamps on the straight line passing through aperture. If one of the lamps is screened, only the light opposite that lamp in the dark will vanish. When the screen is moved away from the lamp, that light will return to its place. Whichever lamp is screened, only the light facing it in the [dark] place will disappear. When the screen is removed, the light will return to its place.
Now this fact may be easily examined experimentally at any time [in the following way]. Let the experimenter employ a chamber with a two-panel door in a dark night, and let him bring several lamps which he should set up at different points in front of the door. The experimenter should enter the chamber, close the door but leave a small gap between the panels, and observe the wall opposite the door. On it he will find separate lights, in the same number as the lamps, which have entered through the opening at the door, each facing one of those lamps. If the experimenter then screens one of the lamps, the light facing it will vanish; and upon his lifting the screen, that light will return. If he covers the opening at the door, leaving only a small aperture facing the lamps, he will again find on the chamber’s wall the separate lights in the number of those lamps, all according to the magnitude of the aperture.
Now all the lights that appear in the dark place have reached it through the aperture alone, and therefore the lights of all those lamps have come together at the aperture, then separated after passing through it. Thus, if lights blended in the atmosphere, the lights of the lamps meeting at the aperture would have mixed in the air at the aperture and in the air preceding it before they reached the aperture, and they would have come out so mingled together that they would not be subsequently distinguishable. We do not, however, find the matter to be so; rather the lights are found to come out separately, each being opposite the lamp from which it has arrived.
In my book, I follow the description of the experiment with this commentary:
“This experiment embodies all the elements of Ibn al-Haytham’s method of inquiry. He begins by stating the problem or question: do lights rays affect each other when they intersect? Next, he gathers information by observing how light behaves in various circumstances. Based on these observations, he offers a possible answer, or hypothesis: lights rays are able to intersect without being affected by each other. He then constructs a simple experiment to test this hypothesis, forcing the lights from different lamps to cross at a single point. After repeating his experiment and confirming his results, he finds that the evidence supports his hypothesis. This systematic, step-by-step approach, based on both sound logic and observed fact, would come to be known as the scientific method. It is the method of inquiry that scientists around the world continue to use in various incarnations, to this day.”
Nowhere does Ibn al-Haytham describe projecting a picture-like image on a screen, but the apparatus described above would lead to that result, if placed in a window or other location. I write:
“By arranging several different light sources across a large area, Ibn al-Haytham leaves little doubt that an image is being projected onto the screen, even if it is only an image of lights. In the second version of his experiment, where he talks about arranging lamps outside a door, Ibn al-Haytham can be said to be describing the first camera obscura because he is projecting an image from outdoors onto a screen indoors.”