Paul Cobb

In my blog on the Silk Roads exhibition, I said that the book in The Book and the Knife series stands for the knowledge of the Islamic scholars such as Alhacen, who made huge advances in science in the East, Africa and Spain, during what we often refer to as the ‘dark ages’ in [northern] Europe. Alhacen features at the start of Thegn of Berewic and is one of the real figures from history who rub shoulders with my fictional characters, in this case Samra and Felip. 

Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham, whose theorem about vision in his Book of Optics is shown above and whose name is usually Latinised into Alhacen, was born in Basra in modern day Iraq in the year 965 CE and lived mainly in Cairo, Egypt. A scientist, mathematician, philosopher and astronomer, such was his later renown in mediaeval Europe that he came to be known simply as ‘the scientist’. Alhacen also got the nickname Ptolemaeus Secundus ("Ptolemy the Second"), in honour of the second century Greek astronomer and geographer whose teachings became influential in medieval thought. 


Astrolabes such as this one made in Moorish Spain in 1067 were used to make astronomical measurements and in navigation for calculating latitude. First made around 150 BCE in Greece, they were further developed by Islamic scholars (source: Wikipedia) 

The Almagest, Ptolemy’s great work on astronomy, was lost to the west after the decline of Greece and was only ‘discovered’ in the 12th century when scholars such as Gerard of Cremona obtained copies and translated them from Arabic into Latin. Yet a few copies of the Almagest had survived in the Muslim world, finding their way from Alexandria to Baghdad, then later copies coming to Cordoba and Toledo in Moorish Spain. The Almagest was well known to Alhacen, who wrote a non-technical explanation of it in his work ‘On the Configuration of the World’. 


Ibn_al-Haytham, known to the west as Alhacen as hisn portrait appears on an Iraqi banknote (source: Wikipedia) 

However Alhacen was no hero worshipper – in a book published between 1025 and 1028 he pointed out various contradictions he found in Ptolemy’s works, particularly in astronomy. Ptolemy had acknowledged that his theories on the motion of the planets, and his hypothesis on their actual configurations, didn’t always match up. He didn’t see it as a problem – but Alhacen did, and he said, “for a man to imagine a circle in the heavens, and to imagine the planet moving in it, does not bring about the planet's motion”. Ouch! 

It is in this book, ‘Doubts Concerning Ptolemy’, that Alhazen sets out his views on the need to question existing authorities and theories. In Thegn of Berewic, in a paraphrase of this Samra quotes him: 

‘If you study the writings of those that came before you, and blindly put your trust in them, you are wrong. You should question what you read; human beings are fraught with all kinds of imperfection and deficiency. It is hard to find the truth, and the road to it is difficult.’

Just how imperfect human beings are was demonstrated to Alhacen in Egypt in 1011, when (quoting from Thegn of Berewic again):

‘[My] renown… brought me to the caliph’s attention, who thought I might use my science to dam the Nile and control its flooding. It was only the gift of Sophia of a kind of madness that saved my life, as you know, when I told him this would be impossible. A ruler who thinks that as a scientist you are a god is as dangerous as one who thinks you are a devil.’

Alhacen was kept under house arrest by the caliph until 1021, during which time he wrote his great ‘Book of Optics’, and later was to come to Spain. In the novel, it is here that he meets and works with my character Samra, the Jewish astronomer and healer, and also Felip, the monk who translates some of The Book of the series title from Arabic into Latin. The work of these three is written into the book, and the book then… well, no spoilers, if you haven’t read that far yet! But the important thing here is that the knowledge in the book in my story ‘… of astronomy, optics, mathematics, medicine… so far beyond what we have…’, as Felip tells Gilbert, is being discovered and brought to northern Europe in the 11th century – in reality, as I’ve said, it came 100 years later.


The structure of the human eye according to Alhacen (source: Wikipedia) 

Alhacen died in Cairo on March 6th 1040 CE. In Thegn of Berewic, he has left Samra to return there, dying a matter of weeks before she is able to demonstrate that he was right about the exact date of the next transit of Venus. Her admiration for him is well-founded, and in my novel she says this of him:

‘He knew the stars in the sky and the motions of the planets in as much detail as he knew the workings of the eye that beholds them. Alhacen saw the science of numbers and the properties of the material world as a child might see its toy bricks; to be picked up and arranged again and again in so many patterns, yet never losing the joy of it.’

This great scholar deserves to be better known today, and he is certainly in the hall of fame of scientists and seekers after knowledge through the ages. Alhazen was a pioneering scientific thinker who made important contributions to the understanding of vision, optics, colour and light. His methodology of investigation, in particular using experiment to verify theory, shows certain similarities to what later became known as the modern scientific method. From his knowledge of optics alone he could have built a telescope 600 years before Galileo!

But where did this knowledge of the world, from the workings of the eye to the motion of the planets, fit with his faith? Let Alhacen himself answer that;

‘I constantly sought knowledge and truth, and it became my belief that for gaining access to the effulgence and closeness to God, there is no better way than that of searching for truth and knowledge.’

Stars that have Arabic names (source: Wikipedia) 

For a great book on how the ideas of three scientists of antiquity (Euclid, Galena and Ptolemy) survived into the middle ages and beyond to inform our modern knowledge of the world, read ‘The Map of Knowledge – How Classical Ideas Were Lost And Found; A History In Seven Cities’ by Violet Moller (Picador 2019). A colourful and fascinating travelogue of thought.