This period saw the work of three extraordinary men, and my school history lessons told me nothing about them.
One of the men was one of the most influential philosophers of the islamic world. His updating of the ideas of Aristotle was to influence christian, jewish and muslim thought for the next few hundred years. He also wrote a medical encyclopedia that was the standard text in Europe and the islamic world for the next half-millennium.
Another was a renaissance man four centuries ahead of his time. His wide-ranging interests included anthropology, pharmacology and mineralogy. He devised a way to measure the circumference of the Earth, which he did to an accuracy of within two hundred miles.
The third can be reasonably described as the founder of the scientific method. He established the practice of developing a hypothesis and using reproducible experiments to test it, to verify or disprove it. He was called ibn al-Haytham, and will be the subject of the rest of this post.
He was born in Basra in what is now Iraq in 965. He moved to Egypt in the early 1000’s and stayed there for the rest of his life. He died in about 1040.
Caliph al-Hakim of Egypt had established a university in Cairo in 1004, and supplied it with a huge library, known as the House of Knowledge or Dar al-Hikmah in arabic. He so wanted to encourage learning that access was open to all and free pens, ink and inkstands were available to those who studied there. Ibn al-Haytham already had a reputation as an impressive thinker, and as he lived in the interconnected arabic-speaking world, he was invited to join the academic community in Cairo, over 1500 miles away.
He was asked to investigate damming the River Nile, in order to regulate the regular devastating floods. On arrival, he soon came to the conclusion that the project was beyond any technology at his disposal. This presented a problem. Caliph al-Hakim did not have a reputation for stability when things didn’t go the way he wanted. One of his nicknames, which was almost certainly not said to his face, was the mad caliph. He once ordered all the dogs in Cairo to be killed because their barking bothered him. Rather than bring the bad news to the caliph, Ibn al-Haytham decided to feign madness himself.
For this he was put under house arrest in Cairo, which turned out to be a blessing in disguise. He had the resources of the new university and its enormous library nearby, and space to think his own thoughts. One of the subjects he addressed was optics. The ancient Greeks had attempted descriptions of the way humans see things. Plato and Euclid had proposed that rays travel out from the eyes towards the object we look at, and then bring the visual information back to the eye. Ibn al-Haytham raised a simple objection to this: in that case, why does it hurt our eyes when we stare at the sun?
Instead, he proposed another hypothesis, that the eye is able to receive light rays that come from the object, and to translate the information they bring into a visual image. He proposed that light rays travel in straight lines from the distant object to the eye. Others had pondered along these lines, but he then went a further, pioneering step. He set up repeatable experiments to test his hypothesis, and documented them. He looked through a straight tube to show that the light from the object travels in a straight line. He set up a pinhole camera, and placed a candle in front of it. He demonstrated that the light from the top of the candle travels through the pinhole to the bottom of the receiving chamber, and light from the bottom of the candle travels through the pinhole to the top. And so the image appears upside-down. Not only did he record his results, he set up ways for others to test and verify or disprove them.
A diagram of the eye from Ibn al-Haytham’s Book of Optics.
He championed enquiry, not taking other people’s word for it (no matter how eminent they are), and relying on one’s own investigations. And so Ibn al-Haytham is considered by many to be the founder of the scientific method.
As well as optics and engineering he wrote on astronomy, philosophy, theology and more. Even number theory. One hypothesis he put forward about prime numbers was finally proven to be correct by the Swiss mathematician Leonhard Euler, eight hundred years later. A geometrical problem he proposed was solved algebraically in 1997.
When his writings were translated into latin and became accessible to the west, his name was latinised as Alhazen. In the thirteenth century the English scholar Roger Bacon and the Polish philosopher Erazmus Witelo wrote extensively on optics after reading his books in translation.
“The duty of the man who investigates the writings of scientists, if learning the truth is his goal, is to make himself an enemy of all that he reads, and,.. attack it from every side. He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency.”
And until I started researching for this blog I had never heard of him.
PS The physicist Jim al-Khalili named these three men as the greatest muslim scientists of all time and among the top ten in the world. Here is a link to his presentation to the Royal Society explaining why.