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pages/chapter1-early-theories-of-light.mdx

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 Our natural perception of space by itself is that of an emptiness. Objects, like ourselves and the surrounding bodies of atomic matter, the Earth, the planets, etc., are considered to fill with their volumes appropriate bites of the empty space. These objects are naturally conceived as consisting of continuous dense matter. The emptiness of space is also deduced from the fact that space does not resist the motions of these bodies, that space is transparent to them.
 Hence, apart from the geometrical property of being naturally three-dimensional, empty space should not have any physical properties.
 
-The wave theory of light was developed by Christian Huygens (1629-1695) in his Traité de la Lumière (presented to the French Academy in 1678 and published in 1690). The theory had to specify the substance carrying the light waves. This substance must flll the whole space, because "holes" for the light were not known. It must also be transparent to the motions of bodies, thus highly diluted of matter. This thinness was expressed in the name "ether", given to the carrier of light waves.
+The wave theory of light was developed by Christian Huygens (1629-1695) in his *Traité de la Lumière* (presented to the French Academy in 1678 and published in 1690). The theory had to specify the substance carrying the light waves. This substance must fill the whole space, because "holes" for the light were not known. It must also be transparent to the motions of bodies, thus highly diluted of matter. This thinness was expressed in the name "ether", given to the carrier of light waves.
 
 The velocity of light was first calculated by Olaus Roemer (1644-1710) in 1676 from the observed eclipses of Jupiter's satellites. The obtained value was very close to 300 Mm/s. The wavelengths of the light-waves were not yet measured then, but they were known to be short. With the velocity of light, exceeding the highest known velocities of waves in matter by a factor of $10^5$, the frequencies of the light waves must have been considered tremendously high, as compared with the known frequencies of sound. Therefore, the elastic moduli of the etherous carrier of light had to be assumed to exceed the elastic moduli of steel by thousands of times. Hence, from its very inception the ether was carrying the intolerable contradiction between the requirements to be as empty as the vacuum space, and much stiffer than steel.
 
@@ -30,7 +30,7 @@ In spite of the inconsistencies of the ether model, it provided the expected ser
 
 ### 1.3 Lack of ether winds around Earth and the fiasco of the ether concept
 
-The velocity of Earth in her motion around the Sun was first calculated by James Bradley (1693-1762). In 1728 he discovered the aberration of starlight and interpreted it as due to this motion. From the value of the aberration (up to 20.5 seconds of arc per year) Bradley found that the orbital velocity of Earth should be $10^-4$ of the velocity of light, i.e., ~30 km/s. It was therefore expected, that the motion of Earth in the ether should cause measurable ether currents or winds flowing around the Earth. Attempts to detect ether winds, also with the use of interference methods (e.g., by Jacques Babinet, 1839) were unsuccessful.
+The velocity of Earth in her motion around the Sun was first calculated by James Bradley (1693-1762). In 1728 he discovered the aberration of starlight and interpreted it as due to this motion. From the value of the aberration (up to 20.5 seconds of arc per year) Bradley found that the orbital velocity of Earth should be $10^{-4}$ of the velocity of light, i.e., ~30 km/s. It was therefore expected, that the motion of Earth in the ether should cause measurable ether currents or winds flowing around the Earth. Attempts to detect ether winds, also with the use of interference methods (e.g., by Jacques Babinet, 1839) were unsuccessful.
 
 The first experiment able to prove decisively that ether winds do not exist was the experiment by A. A. Michelson (1852-1931) and E. W. Morley (1838-1923), published in 1887. In their experiment, light from a monochromatic source was split into two beams, parallel and perpendicular to any direction of Earth's motion. After passing adjustable, slightly different optical paths, the two beams were brought together to produce their interference fringe pattern. Then the whole apparatus was turned by 90°, so that the two beams exchanged the directions of their paths. If there were a difference between the velocities of light along the two paths, then during the exchange of orientation of the two beams their interference fringe pattern should have been shifted. Although the apparatus was capable of measuring a fringe-shift smaller than the expected one, none was found. The experiment was performed at different seasons and locations, and no difference could be found in the velocity of light in directions along the expected ether wind, opposite to it, or perpendicular to it. Therefore, there are no ether winds or currents; hence, there is no ether.