An Arab scholar, Al-Hussein ibn Sina, once said in the eleventh century:
"Air is either an organ or a medium; it does not come into contact with the stars we see. If it is an organ, then it possesses the capacity for sensation or serves as a transmitter. But the claim that air, through alteration, becomes endowed with sensation, perceives the stars, and conveys what it senses to vision is absurd."
That air could become an organ was unacceptable to any rational person. Or rather, light was a form spread through the air and celestial spheres, combining with our vision and becoming its organ.
If we tolerated such a detestable claim, we would be unable to see the stars in their entirety. Furthermore, according to these people, how powerful would our eyes have to be? Powerful enough to turn the air and light distributed among those celestial spheres into a sensation-endowed faculty—or whatever sort of faculty one wished to call it!
Moreover, air and light were not connected to one person's vision but not another's. So why would these two things convey what they perceived to one person and not to another?
Thus, the condition for vision was that the object seen entered the pupil, while the air conveyed what it perceived to sight. The sensation of air would not be the cause by which sensory things reached the soul, but rather the reason vision stood at a certain proportionate distance from the visible object, because air was the medium situated between the two.
According to Eugene Beauharnais, when Napoleon retreated from Jaffa to Cairo with a small detachment, they saw a mirage in the desert. Not only did the men see it; the camels saw it too. Those thirsty beasts charged desperately toward the illusion, impossible to stop. Later,