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

ANOTHER ILLUSION

Not all illusions of view, we are able to explain. Often and cannot guess what kind of inferences are made unconsciously in our brain and cause one or another illusion. In figure 1 are clearly visible two arc which is convex to each other. Don't even doubt that this is so. But you only have to attach a line to these imaginary arcs or to look at them along, holding the piece at eye level to ensure their straightness. To explain this illusion is not so simple.


Figure 1. The middle two lines running from right to left, parallel direct, though seem arcs convex to one another.

The illusion disappears 1) if, raising the figure to the level of eyes to look at her so to gaze slid along the lines 2) if, placing the end of the pencil in any point of the shape, keep your eyes on this point.

Specify a few examples of illusions in the same way. Figure 2 direct seems to be divided into unequal segments, the measurement will convince you that the segments are equal.


Figure 2. On whether 6 segments of radulina this straight?

Figure 3 and 4 parallel lines are represented non-parallel.


Figure 3. Parallel lines seem to be non-parallel.


Figure 4. Modification of illusions Fig. 3.

Figure 5 circle gives the impression of an oval


Figure 5. Circle it?

It is remarkable that optical illusion, shown in Fig. 2, 3 and 4, stop deceiving eyes, if they are considered in the light of the electric spark. Obviously, these illusions are associated with eye movements: at the brief flash of sparks such movement does not occur.

That's no less interesting illusion. Take a look at Fig. 6 and say what dash is longer - the ones on the left, or those in the right part? First appear longer, though both are strictly equal (Drawing represents, by the way, the illustration of the geometric principle of Cavalieri; area occupied by both parts of the "pipe", equal). The illusion is called the illusion of a "pipe".


Figure 6. The illusion of "pipe". Right dash seem shorter than equal to them left.

Entertaining physics J. Perelman

 




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