Written by OPARAKU DIVINE C. and SUNKANMI AROGBOKUN OD.
Is it not funny how Science claimed to have answers to everything? The most comical is representing lines as light rays, while making us to see the crystalline lens as this glass thing with an amount of refractive tendencies and powers. As if it were not enough. Again, were we told by science that the vascularized yellow pinkish tissue behind the eye is what? A film! Yeah, a camera film that images are implanted on. Finally, we were bewitched that this film-acting structure sends some electrical signal, are you playing? through some imaginary channels to the brain. Okay, I learnt they were not imaginary, CT scan could pick them, fine, I have seen it before; the visual pathway. But how do you explain the electric current? Believe me it was explained, in a speech given by Science, titled Electrophysiology of Vision. Who then speeched the afore? At least I now know Science lay claim to electrophysiology. How about the earlier jargons, yes that one that has to do with glass, lens, rays and blah blah blah. Oh, you said? Ahn? It was who? Oh Optics! Optics did?
Somewhat more than a century and a quarter past, Dugald Stewart, philosopher and critic second only to Sir William S Hamilton, wrote: In considering the phenomena of perception, it is natural to suppose that the attention of philosophers would be directed, in the first instance, to the sense of seeing. The variety of information and of enjoyment we received by it; the rapidity with which this information and enjoyment are conveyed to us; and above all, the intercourse it enables us to maintain with the more distant part of the universe, cannot fail to give it, even in the apprehension of the most careless observer, a preeminence over all our other perceptive faculties. Hence it is, that various theories, which have been formed to explain the operations of our senses, have a more immediate reference to that of seeing; and that the greater part of the metaphysical language, concerning perception in general, appears evidently, from its etymology, to have been suggested by the phenomena of vision.
OPTICS AND THE NATURE OF LIGHT
For most of human history, the facts of light and optical phenomena have been seen as central to the understanding of Nature. A historical review of ideas about light could certainly fill many books- no such attempt will be made here. Some of the central facts about light that have been understood long before physics include:
(i) Sources of Light: Light is emitted by hot bodies; moreover, intense light also feels hot (we would now say that it carries energy, which heats any object absorbing this energy). Light rays vary enormously in their intensity.
(ii) Propagation: Light travels in lines, or ’rays’, that are straight, in any homogeneous medium through which it does travel - it does not apparently ’fall’ in the earth’s gravity, unlike ’material’ bodies. When it does curve or change direction, this is invariably because the medium through which it travels is inhomogeneous. It can travel through gases, and many liquids and solids - which are classified as transparent, translucent, or opaque, depending on the facility with which light passes through them. And crucially - light travels through a complete vacuum, apparently over limitless distances, requiring no material medium for its propagation.
(iii) Interaction with matter: Light is partially refracted upon passing through the interface between two transparent media, thereby abruptly changing in direction; and it is also partially reflected. The reflection is specular off a smooth surface. Thus in general we have simultaneous reflection and refraction at the smooth boundary between two transparent media. If light meets an opaque medium it is either absorbed or scattered (ie., reflected in many different directions). A smooth opaque medium can reflect it specularly.
(iv) Self-Interaction: Light apparently does not interact with itself - if two light beams pass through each other, they do not appear to influence each other at all. This result is of great significance, and yet it is usually thought to be so obvious that it is totally ignored (we take for granted that when we look at some object, this in no way affects what somebody else sees when they look at another object, even though the light rays involved can clearly cross each other).
(v) Speed of Propagation: Light travels incredibly fast (until the measurements of Rømer in 1660, it was not clear that it traveled at all - the fact of light emission led most to suppose this, but it does not force this conclusion). By the Renaissance it was generally considered that light traveled from an object emitting, or reflecting/refracting the light, to the eye. But this was not obvious, and indeed the view until the work of the Islamic astronomer/mathematician philosopher Alhazen was that it traveled from the eye to the object.
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