I knew this moment would come eventually! As an amateur scholar of the history of science, I've dreaded the day that I get my facts screwed up enough to bring commentary from an actual historian. Well, that day has come -- after reading my talk on "Forgotten milestones in the history of science", ThonyC of The Renaissance Mathematicus sent me a nice email pointing out how I'd bungled my discussion of the significance of Ibn al-Haytham's work.
I knew I was on shaky ground while I was working on that section of the talk, which was the hardest to prepare. I was working from a limited amount of sources against a deadline to complete the talk, but I really wanted to include al-Haytham as perhaps the most significant optics researcher of his era. Most of my colleagues in optics are unaware of the history of optics before Newton, and this was a great opportunity to bring a little attention to that era and the interesting philosophical questions pondered.
There's nothing that bugs me more than incorrect information, and spreading said information, so I thought I'd try and correct at least some of my mistakes with the help of Thony's comments via email!
In my talk, I described two early theories of vision, namely a theory of "forms" and an "emission" theory. Thony notes,
You start by describing only two of the Greek optical theories whereas there were at least six (!) influential ones, all of which were known to al-Haytham. These are in chronological order, the atomist (intromission), the Platonic (mixed), the Aristotelian (intromission), the geometric [Euclid, Hero and Ptolemaeus] (extromission), the Stoic (mixed!) and the Galenic, which was a modified Stoic theory. al-Haytham’s greatest achievement was to demonstrate clearly that an intromission theory of vision was fully compatible with the strictly mathematical geometric theory of Euclid et. al.
This was a sin of omission on my part; for a short talk on a variety of topics I'm not too bothered by my oversimplification, but I'll be sure to revise my talk to note that the theories in Greek thought were much more diverse and subtle.
I wrote that al-Haytham, "Provided the first description of the scientific method." This is also a horrible oversimplification! Let me quote Wikipedia (not necessarily the best source, either) to highlight the fact that the development of the scientific method was a long process that can't be tied to any one person:
The development of the scientific method is inseparable from the history of science itself. Ancient Egyptian documents describe empirical methods in astronomy, mathematics, and medicine. The ancient Greek philosopher Thales in the 6th century BC refused to accept supernatural, religious or mythological explanations for natural phenomena, proclaiming that every event had a natural cause. The development of deductive reasoning by Plato was an important step towards the scientific method. Empiricism seems to have been formalized by Aristotle, who believed that universal truths could be reached via induction.
There are hints of experimental methods from the Classical world (e.g., those reported by Archimedes in a report recovered early in the 20th century CE from an overwritten manuscript), but the first clear instances of an experimental scientific method seem to have been developed in the Arabic world, by by Muslim scientists, who introduced the use of experimentation and quantification to distinguish between competing scientific theories set within a generally empirical orientation, perhaps by Alhazen in his optical experiments reported in his Book of Optics (1021). The modern scientific method crystallized no later than in the 17th and 18th centuries.
Even this is likely a too simple explanation of the history! When I gave my talk, I had a significant number of questions about al-Haytham's era, which I could not satisfactorily answer. My impression is that describing the history of scientific methodology in that early era is quite challenging.
I stated in my talk that al-Haytham, "Introduced rectilinear propagation of light." This is also a statement oversimplified to a nonsensical statement. It would be more proper to say that he did many experiments to test the idea of rectilinear propagation.
In my statement that al-Haytham was, "First to recognize that the brain is the center of vision, not the eye," Thony notes that that milestone goes back to Galen (129-199).
Even my statements about the camera obscura are incorrect! I stated that "No naturalists apparently had studied the phenomena systematically," which seems more or less true... in the Western world! Chinese philosopher Mo-Ti (470-390 B.C.E.) had observed an inverted image produced by light passing through a pinhole into a darkened room, which he referred to as a "locked treasure room".
In my defense, my impression is that Mo-Ti's work did not influence Western scientific thought, and I semi-consciously excluded Eastern scientists from my discussion. Ibn al-Haytham seems to be the first "Westerner" to construct a camera obscura and test its effects, though as I noted in the talk ancient Greeks had noticed the unusual properties of light passing through pinholes.
Fortunately, I seem to have more or less bungled only two of my slides -- though they're important ones!
Hopefully you can see from the above observations that I've learned a lot already from my mistakes! Even from the short discussion with Thony I've been introduced to a lot of historical figures and ideas that will be interesting to explore, and hopefully blog about, in future posts. (I've been thinking of blogging about al-Haytham, but haven't felt knowledgeable enough to do it -- apparently I have lower standards for talks.)
It is also enlightening to see how complicated the history of science gets back in the pre-Renaissance era! I described my own attempts to understand this era as "wandering deeper and deeper into a treacherous (but fascinating) swamp"! It is relatively easy to understand the philosophy, culture and preconceptions of a 19th-century scientist, but much harder to do so with a 10th-century one. This is, however, what makes the earlier scientists so rewarding to study.
Anyway, thanks to Thony for pointing out my mistakes! I appreciate the criticism, and hopefully I've straightened out the record somewhat!