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


In the novel "invisible Man" English writer wells seeks to convince his readers that the ability to become invisible is quite feasible. His hero (the author of the novel presents him to us as "brilliant physics, which ever saw the world") has opened a way to make the human body is invisible. Here is how he sets out his friend, the doctor bases his discovery:

Visibility depends on the action of visible bodies on the light. You know that body or absorb light or reflect it, or break. If the body does not absorb, not reflect or refracts light, it may not be visible by itself. See, for example, opaque red box because the paint absorbs some light and reflects (scatters) the remaining rays. If the mailbox does not have absorbed any share of the light and reflected it all, he seemed to have shiny white box, silver. Diamond mailbox absorbed little light, its total surface would reflect its also a bit; only places on the edges, the light would be reflected and refracted, giving us a brilliant visibility sparkling reflections - something like a light skeleton. Glass box shone less would not be so clearly visible, as a diamond, because it would be less reflection and less refractions. If you put a piece of ordinary white glass in water and, especially, if you put it in some liquid denser than water, it will disappear almost completely, because the light entering through the water on the glass, refracted and reflected very poorly. The glass becomes as invisible as the stream of carbon dioxide or hydrogen in the air, for the same reason.

"Yes, " said Kemp (the doctor), it's all very simple and in our time, is known to every schoolboy.

- And here is another fact, known to every schoolchild, If a piece of glass crushed and turned into a powder, it becomes much more visible in the air, he becomes an opaque white powder. This is because the pounding multiplies the verge of the glass, producing reflection and refraction. The plates are only two sides, and powder light is reflected and refracted by each grain, which passes through and through the powder it penetrates very little. But if the white crushed glass to put in water, it immediately disappears. Crushed glass and water have approximately the same refractive index, so switching from one to another, the light is refracted and reflected very little.

Putting the glass in some liquid with almost the same refractive index, you make it invisible: any transparent thing becomes invisible if placed in an environment with the same with her refractive index. Enough to think just a little bit, to make sure that the glass can be made invisible in the air: it is necessary to arrange so. To its refractive index equal to the refractive index of air, because then, passing from glass to air, the light is neither reflected nor refracted at all*.

"Yes, Yes, " said Kemp. "But man is not that of glass.

- No, he's more transparent.


And it says the naturalist! Do in ten years you had quite forgotten physics? Paper, for example, consists of transparent fibers, it is white and impenetrable for the same reason white and impenetrable glass powder. Will nemalite white paper, fill with oil the spaces between the fibrils so that the refraction and reflection took place only on the surface, and the paper becomes transparent as glass. And not only paper, but also fiber fabrics, wool fibers, fiber tree, our bones, muscles, hair, nails and nerves! In short, the whole structure of man, except the red substance in his blood and the dark pigment of the hair, everything is made of transparent, colorless tissue; this is how much makes us visible to each other!"

Confirmation of these considerations may serve the fact that not coated animals albino (fabric which does not contain coloring substances) are largely transparent. Zoologist, found in the summer of 1934 at the Children's Village instance white frog albino, describes it thusly: "the Thin skin and muscle tissue Shine: visible inside the skeleton... Very well frogís the albino visible through the abdominal wall contraction of the heart and guts".

Mountain novel by H. G. wells invented a way to make transparent tissue of the human body and even his colorants (pigments). He successfully applied his discovery to his own body. The experience has been brilliant, the inventor became completely invisible. About the future of this invisible man we now know.

* Full stealth is completely transparent object we can achieve, if you surround it with walls, light-scattering strictly evenly. Eyes who looks inside through a small hole, you will then receive from all points of the subject just as much light, as if the subject does not exist: no glare or shadows will not detect its presence.
That's as may be furnished with a similar experience. Funnel, two feet in diameter, made of white cardboard set, as shown in the figure, at a distance of 25-svetovoy light bulbs.

Invisible glass rod.
Below enter the glass rod as possible vertically. The slightest deviation from the vertical position does what wand seems dark axis and light at the edges or, on the contrary, the light axis and the dark at the edges. Both paintings lighting one into the other with a light changing the position of the sticks. After a number of samples it is possible to achieve a completely uniform illumination sticks, and then she eyes looking through a narrow (no wider than 1 cm) lateral hole, disappear completely. In this environment, the experience is complete invisibility glass object, despite the fact that its refractive ability is very different from the refractive ability of the air.
Another technique which you can use to make the invisible, for example, a piece of cut glass, is to put it in a box, covered inside with luminous paint.

Entertaining physics J. Perelman


System Orphus


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