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J. Perelman
"Entertaining physics". Book 2.
Chapter 9. Reflection and refraction of light. Vision


If you say that in your field of vision is the plot, which you did not see, although he is right in front of you, you will certainly not believe. Is it possible that our entire lives are not noticed such a major lack of vision? Meanwhile, here's a simple experience that will convince you.

The figure for the detection of the blind spot.

Keep the picture posted above, at a distance of 20 centimeters from your right eye (closing the left) and look at the cross, placed on the left; slowly zoom in the picture to the eye: will come a moment when a big black stain on the intersection of the two circles disappear! You won't see it, although it will remain within the visible area, and both circles to the right and to the left of it will be clearly visible!

This experience, first produced in 1668 (in somewhat different form) famous physicist MARRIOTT, was very amused by the courtiers of Louis XIV. MARRIOTT did the experience: put two nobles at a distance of 2 meters against each other and asked them to consider one eye some point side, then each seemed that his opponent has no head.

Strange as it seems, but people only in the XVII century learned that on the retina of their eyes there is a "blind spot", about which nobody had thought. This is the place retina where the optic nerve enters the eyeball and yet not divided into small branching with elements that are sensitive to light.

We do not notice the black hole in our field of vision due to long-term habits. Imagination involuntarily fills this gap details surrounding background; so, in the picture above, we are not seeing spots, mentally continue the line of circles and are convinced, though clearly see the place where they intersect.

If you wear glasses, you can do an experiment: stick a piece of paper glasses (not in the middle, and the side). In the early days of paper will stop to watch, but a week has passed, another, and you are so used to it that it will no longer even notice. However, it is well known to everyone who had to wear glasses with cracked glass: a crack is seen only in the early days. Similarly, due to long-term habits, we do not notice the blind spot in our eyes. In addition, both blind spots correspond to various parts of the field of view of each eye, so that when the vision with two eyes there is no space in their common field of view.

Do not think that a blind spot in our field of view slightly; when you see (one eye) on the house from a distance of 10 m, due to the blind spot, do not see a rather extensive part of its facade, having a diameter more than one meter, it fit the whole window And the sky remains invisible space equal in area 120 drives the full moon!

When looking at building one eye small area With' field of view, corresponding to the blind spot (with) eyes, the us is not perceived at all.

Entertaining physics J. Perelman


System Orphus


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