In the past, it was believed that light had infinite speed, but this theory was gradually being left aside. It was from the time of Galileo Galilei that the idea that light had a very large but finite speed became increasingly plausible. It remained then to know how to determine this value.
One of those who proposed that light had finite speed was Newton, who claimed that when light changed from air to glass, it had its propagation speed. increased, due to the force of attraction on the corpuscles, causing them to approach the normal straight to the surface that separates the air and glass media. Newton also proposed that the denser the propagation medium, the greater the velocity, since the more intense the attraction force on the corpuscles.
In a second moment, the wave model proposed by Huygens and improved by Young considered that the denser the medium, smaller would be the propagation speed of the wave. Huygens reached this conclusion by experimenting with waves in liquid media. Thus, he concluded that the speed of light in air should be greater than in glass medium, and not the other way around, as Newton had initially proposed.
Armand H. Louis Fizeau was a French physicist who, in the year 1849, carried out an experiment in order to determine the speed of light. Louis managed to reach a value 5% above the value we know today for the speed of light. A little later, Foucault made some modifications in the experiment used by Louis and managed to arrive at a more accurate value by determining the speed of light in water and in other media as well. transparent. His results were in line with theory undulatory.
Today we know that the speed of light is approximately 2.998 x 108 m/s, but we approximate it to 3 x 108 m/s.
The wave theory did not provide fully satisfactory explanations for all light phenomena - the characteristics of the light waves and the medium in which they propagated were still considered obscure.
It was then that the theory of ether. This theory was proposed in order to explain what was the material medium for the propagation of light waves. In this theory, the ether was considered an invisible fluid medium that occupied all the empty space of the Universe.
We know that every fluid offers resistance to a material, but it was seen that the ether did not present resistance to the movement of celestial bodies. Thus, a difficulty then arose in characterizing it. To be resistant to this movement, it would be necessary to assume that it had very low density. However, to serve as a propagation medium for a light wave, the ether would need to be both rigid and solid. Thus, until the 20th century this theory was valid, but from then on a new theory emerged, proposed by Einstein, which disregarded the need for a material medium for the propagation of light.
By Domitiano Marques
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/fisica/velocidade-luz-na-refracao.htm