When you are interested in physics you must read “Unbelievable“!
Bradley observed the stellar aberration of the star y-Draconis in 1727. We demonstrated in the previous chapters that the conclusion of science that there could not be dragged ether was premature. The presumption of science that dragged ether could not exist had consequences; the stellar aberration observed occurs so there had to be an other explanation.
The light of a star in a telescope is bent to the focus point. Science assumed, to be able to explain stellar aberration, that the light from the star kept moving sideways in the telescope. When the beams of light from the star hit the lens of the telescope right-angled, then the image of the star would be sideways of the center point because of the assumed continuing sideway movement of the light in the telescope.
The way scientists apparently assumed how stellar aberration was achieved in the telescope is comparable to a bullet aimed at the heart. The victim moves as quickly as possible to the side to avoid the bullet. The bullet hits the heart away from where the shooter aimed because the victim moved sideways. Science argued therefore that if the telescope is filled with water the observed aberration would have to increase. Light travels slower in water than in a vacuum or in air.
Because of the decrease of the speed of light in water one assumed that the light in the telescope, when filled with water, had more time to move sideways and thus the aberration would increase. The speed of light in water is c divided by the index n of water. The index of water is ca. n=1.33. The light of the star will stay longer in the telescope when it is filled with water. The light beam will have more time to move sideways and therefore science expected an increase of the stellar aberration with a factor 1.33.
To resume our analogy with the victim, the victim is now shot with an arrow. The arrow is again aimed precisely at the heart. The victim runs sideways as hard as he can and because the arrow takes longer to reach the heart, the spot where the heart is penetrated must lie further sideways. The victim has more time to move sideways before the arrow spears his heart.
In 1871 Sir Geofry Air conducted this experiment. He, however, did not measure any increase in aberration. The aberration of the star was the same with or without the telescope filled with water! This was not a really big surprise, because in 1818 Fresnel had postulated that there would be a “drag-factor”.
Fresnel came to this conclusion after Arago had observed that the earth always seems to be “at rest” in the ether. But science had concluded earlier that the dragged ether did not exist. A drag factor had to be introduced to “explain” the contradiction between “always at rest in ether” (Arago) and the presumed “non-existence” of the dragged ether.
Now science should have wondered whether this was correct. Apparently science was so fixated looking for absolute ether, that this obvious sign was ignored. So to explain the lack of increase in stellar aberration when the telescope was filled with water, a drag factor had to be introduced!
The above is a very short historical overview of the attempts of scientists to explain stellar aberration. Finding any logic in the above is difficult. Weird concepts were proposed by scientists to explain the phenomena, because the only logical explanation was denied.
The drag factor of Fresnel is:
f is the drag factor of Fresnel and n the refractive index.
In general one can state that in the 19th century physicists were strongly convinced there was absolute ether in which light moves in all directions with the same speed c. The ether was assumed to be absolute because experiments indicated that whatever the circumstances the speed of light was always c. The absolute ether was by then the presumed medium existing in vacuum by means of which light propagates. The absolute ether is considered to be at rest while all the stars and planets move in comparison to the absolute ether. When the ether cannot be influenced by anything than this ether is absolute. Only if the earth is at rest in the absolute ether then light will travel with equal speed in all directions. When the earth is moving in the absolute ether, the speed of light cannot be the same in all directions because the light moves in the ether in all directions with c. When the Earth moves relative to the ether on Earth the speed of light cannot be c in all directions because the light moves in the absolute ether in all directions with c; you cannot have both at the same time.
In experiments it was observed that the speed of light was always c in all directions. The dragged ether was denied and therefore the only possible form of ether left was the absolute ether. Because the Earth in her path around the Sun cannot always be at rest with the absolute ether there must be a physical process explaining why the Earth appears to be at rest with the absolute ether. The drag factor of Fresnel was a possible explanation.
Next chapter: The experiment of Fizeau