Reflection and refraction of light refers to the number of physical phenomena discovered as a result of direct observations, without conducting laboratory experiments. For the first time they started talking about him in Ancient Greece, but most physicists are inclined to believe that this fact was known earlier. Just the first scientist who tried to give a logical explanation of a number of facts established empirically was Cleomed, who lived in the 1st century AD in what is now Greece. Before him, Euclid described this phenomenon, observing a ring lying on the bottom of the jug, which was not visible to the observer at a certain angle, but if you start pouring water into the jug, then after some time without changing the angle of view, the observer could see the ornament lying on the bottom. But since Euclid still did not give a detailed explanation of this experiment, Cleomed is considered the first scientist to study refraction in detail.
The subject of his research was the refraction of light in water - he noted that if a long stick was lowered into water so that a certain part of it continued to remain above the surface, visual refraction occurs at the interface between air and water. But in reality, the stick remains intact, which means that the reason for this optical effect is visual illusion?
Studying this phenomenon more closely, Cleomed noted that if a light ray enters from a less dense medium into a denser one, while having an oblique direction (that is, having an angle relative to the boundaries of two media), then a medium with a higher density deflects it to a sheer direction.
It was by such a refraction that he explained the possibility of seeing the Sun for some time after sunset.
Kleomed 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 picture of the general laws of the process. In the future, another ancient Greek scientist, who lived a century later than Cleomedes, continued the scientific research begun by his predecessor, and almost came close to unraveling the physical laws by which a light ray is refracted.
After conducting a fairly large number of experiments, Claudius Ptolemy was able to establish the approximate angle at which light is refracted in a particular medium. So, for the refraction that occurs when a light beam passes from the depth of water into glass, the angle of refraction is 0.88 of the angle of incidence. For other environments, this value changes - for air and water it is 0.76, and for air and glass it is 0.67.
But it took several centuries to fully establish the laws by which the refraction of light proceeds. More than one generation of scientists has been improving their knowledge, and the final version of the light refraction formula is attributed to Rene Descartes, the most famous French natural physicist.
In the original edition 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 defined media is constant and unchanged 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 research and description of the refraction of a light beam when it enters from one medium to another, as already mentioned, Rene Descartes. He made a comparison surprisingly correctly characterizing the essence of the process of refraction of light, comparing it with a ball flying in the air. If during his flight he comes across a fabric light and thin enough to easily break through and continue moving, he will only lose part of his original speed and slightly change the angle of flight.