Refraction of light - the history of the physical concept

Reflection and refraction of light refers to the number of physical phenomena discovered as a result of direct observations, without conducting laboratory experiments. It was first talked about in ancient Greece, but most physicists tend to believe that this fact was known before. Just the first scientist who tried to give a logical explanation to a number of experimentally established facts was Cleomed, who lived in the 1st century AD in the territory of present-day Greece. Prior to it, Euclid described this phenomenon by observing the ring lying on the bottom of the pitcher, which was not visible to the observer at a certain angle, but if you start pouring water into the jug, then after a while the viewer could see the ornament lying on the bottom without changing the angle of view . But since Euclid did not give a detailed explanation of this experience, Cleomede is considered the first scientist who studied the refraction in detail.

The subject of his research was the refraction of light in water - he noted that if a long stick is lowered into the water in such a way that a certain part of it continues to stay above the surface, visual refraction occurs at the boundary between air and water. But in fact the stick remains intact, so the reason for this optical effect in visual deception?

Investigating this phenomenon more closely, Cleomed noted that if a light beam enters a denser medium from a less dense medium, while having an oblique direction (ie, having an angle with respect to the boundaries of two media), then a medium having a large density deflects it to a steep Direction.

It was by this refraction that he explained the possibility of seeing the Sun for some time after sunset.

Cleomed gave only the most general characteristic and described the refraction of light only in the form of some primitive experiments, which nevertheless give a fairly complete idea of the general laws of the course of this process. Later, another ancient Greek scientist, who lived a century later, Cleomed, continued the scientific research begun by his predecessor, and almost came close to unraveling the physical laws by which the light beam is refracted.

Having conducted a sufficiently large number of experiments, Claudius Ptolemy was able to establish the approximate angle, under which light refraction occurs in this or that medium. Thus, for the refraction occurring when a light beam passes from the depth of water to the glass, the angle of refraction is 0.88 of the angle of incidence. For other media, this value varies - for air and water it is 0.76, and for air and glass 0.67.

But the complete establishment of laws, according to which the refraction of light proceeds, took several more centuries. More than one generation of scientists was engaged in improving existing knowledge, and the final redrafting of the light refraction formula is attributed to Rene Descartes, the famous French naturalist physicist.

In the original version of the Dutch scientist V. Snellius, the formula for calculating the angle of incidence looked like this:

N = sin (a) / sin (b).

In other words, the refractive index of a light beam for two definite media has a constant and unchanging character and is equal to the ratio of the sine of the angle of incidence to the sine of the angle of refraction.

Finally completed the process of studying and describing the refraction of the light beam when it comes from one environment to another, as already mentioned, Renee Descartes. He gave a comparison that surprisingly correctly characterizes the essence of the process of refraction of light, comparing it with the ball flying in the air. If, during his flight, he encounters a light enough and thin enough to break through and continue moving, he will only lose some of his original speed and slightly change the angle of flight.