Monday, February 14, 2011

Ibn Ezra on seeing at a distance

Summary: He follows Galen's extramission theory of sight.

Post: There was an interesting point in the longer essay from Ibn Ezra I presented a few weeks ago on parashat Yitro, that might have been missed. It has to do with sight vs. hearing, and why we see lightning before we hear thunder. Ibn Ezra writes:
והנה ידענו כי הרגשת העין נכבדת מהרגשת האזן. כי ידענו בראיות גמורות כי רגע הראות הברק לעין הוא רגע הרעם רק העין ראתה מרחוק והאויר מביא הקול אל האזן. והליכתו לאט ולא יגיע אל האזן רק אחר עבור הרגע והאותיות שהאדם מדבר בם דמותם נכתב באויר על דרך מוצאם מהחמשה מקומות, לא על דרך המכתב שהוא ביד בן אדם. והנה כל אות הזי"ן נכנס באוזן קודם כ"ף וי"ו רי"ש. והנה אם נאמר פלא היה, שנאמר: זכור ושמור בבת אחת. איך תשמע האזן?!
And behold, we know that the sense of the eye of weightier {more important?} than the sense of the ear. For we know, with complete proofs, that the instant that the lightning is seen by the eye is the same instant as the thunder, but the eye sees from a distance, while the air brings the sound to the ear. And its travel is slow, and it only reaches the ear after that instant. And the letters that a person speaks with, their "image" is written in the air in the way that they are let out from the five places {of articulation}, not by way of writing which is by the hand of man. And behold, {in the word Zachor,} every letter Z enters the ear before the Ch, O, and R. And behold, it we say that it was a wonder, as was stated that Zachor and Shamor were said at the same time, how did the ear hear?
Obviously, we know nowadays that this is not the case, but this is an instance of a Rishon relying on secular knowledge, on the science of the day.

For the sake of comparison, here is what Aristotle said about experiencing lightning vs. thunder -- from a translation of the translation of Shmuel Ibn Tibon.

The same idea of fineness, and fineness of senses, but there is no mention that sight occurs at a distance, while the sound (or sound waves) need to travel, and that that takes time.

But if we look to Empedocles, we would appear to have something akin to what Ibn Ezra mentions:
In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.
It turns out to be a machlokes between Artistotle and Galen:
The eye has been the subject of conflicting interpretations since antiquity.  Many ancient physicians and philosophers believed in the idea of the active eye.  Plato, for instance, wrote in the fourth century B. C. that light emanated from the eye, seizing objects with its rays.  More metaphorically, Aristotle's disciple, Theophrastus, wrote that the eye had "the fire within."  In saying this, he departed from the ideas of his teacher, since Aristotle was among the first to reject the extramission theory of vision.  "In general, it is unreasonable to suppose that seeing occurs by something issuing from the eye," he declared.  Aristotle advocated for a theory of intromission by which the eye received rays rather than directed them outward. 
In the second century A. D., Galen had at least two different theories of the eye to choose from.  He chose the extramission theory because it corresponded well with his image of sight as a function of an optical pneuma, flowing forth from the brain to the eyes through hollow optic nerves.  Galen defined many of the fundamental features of the anatomy and physiology of the eye until the seventeenth century.  Benefiting from the work of the anatomists who dissected in Alexandria, such as Rufus of Ephesus, he described the retina, cornea, iris, uvea, tear ducts, and eyelids, as well as two fluids he called the vitreous and aqueous humors.  He noted some of the peculiar features of sight such as binocular vision.  Galen paid particular attention to the crystalline lens, which he described as a round lens in the middle of the eye.  He concluded:  "the crystalline lens is the principal instrument of vision, a fact clearly proved by what physicians call cataracts, which lie between the crystalline humor and the cornea and interfere with vision until they are couched." 
The eye was a subject of special interest in medieval Islamic medicine and philosophy.  Between the ninth and fourteenth centuries, dozens of specialized treatises on ophthalmology appeared.  Influenced by their readings of Galen, the majority of Islamic scholars, such as al-Kindi and Hunain ibn Ishaq (Johannitius) in the ninth century, favored the extramission theory of sight.  The latter, in such works as Ten Treatises on the Eye and the Book of the Questions on the Eye, elaborated on the series of tunics behind the vitreous humor, paying special attention to the retina, whose role was to nourish the vitreous humor and conduct visual spirit through the hollow optic nerve.  He further reinforced the centrality of the crystalline lens.
Ibn Ezra was presumably following those scholars who favored the extramission theory. But even then, there were Islamic scholars that were challenging this view.


Z said...

What do you mean that nowadays we know that its not the case? We know that the lightning happens at the same time as the thunder. We also know that sound travels thru the air in waves and each sound makes a different wave. I dont think he means that an image of the actual letter is made in the air. That would be ludicrous.

joshwaxman said...

I wrote:

but the eye sees from a distance, while the air brings the sound to the ear.

interpret the other parts however you want. but we know nowadays that just as the sound travels through the air, so does the light travel through the eye. just that light travels through the air faster than sound. seeing does not happen at a distance, but at the eye itself. that is, Ibn Ezra is saying that seeing happens instantaneously due to extramission of rays from the eye.

kol tuv,

Anonymous said...

Does it mean that what's heard depends on what spirit carried it to the ear, whereas what's seen rather depends on the inner qualities of the person seeing?

joshwaxman said...

well, that certainly is a nice thought that one can extract from his words.

still, since the context makes it clear that he is speaking of scientific reality, and since we can identify this contemporary scientific belief as Galenic science, i would not go for any allegorical meaning; nor would Ibn Ezra. :)

kol tuv,

Anonymous said...

Thanks Josh!

(I'm full of nice thoughts. ;)

thenutgarden said...

Another fascinating blog which reminded me of this passage of Zohar:

“The innermost ear is formed of curved apertures so that the sound will be slowed down in entering the brain, the brain will be able to perceive it and it will not enter quickly, for whatever happens quickly does not possess complete wisdom... sound is slowed down in the river of that trickle in the curve of the ears and does not enter quickly. Then it is tested to see whether it is good or bad” (Zohar Ha’azinu on Job 34:3).


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