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Maxwell's idea to measure aether

  1. Sep 28, 2010 #1

    ghwellsjr

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    On this webpage http://www.mathpages.com/home/kmath241/kmath241.htm" [Broken] are these words of Maxwell:

    "The only practicable method of determining directly the relative velocity of the aether with respect to the solar system is to compare the values of the velocity of light deduced from the observation of the eclipses of Jupiter’s satellites when Jupiter is seen from the earth at nearly opposite points of the ecliptic."

    First off, has this been discussed on this forum?

    Secondly, what exactly was Maxwell proposing?

    And finally, assuming that the technology were available to Maxwell, could he have measured something that would have led him to the wrong conclusion?
     
    Last edited by a moderator: May 4, 2017
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  3. Sep 28, 2010 #2

    HallsofIvy

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    Assuming that the earth has a specific speed through the ether, then measuring the speed of light coming from Jupiter (or any object) at opposite points on the ecliptic would, under the right conditions, give values differing by twice the speed of the earth through the ether. Since Michaelson and Morley did similar experiment not long after (on the surface of the earth, not using Jupiter) I imagine that the technology was sufficient (certainly people were getting accurate values for the speed of light using the eclipses of the moons of Jupiter). What he would have gotten would, of course, have been a null result- that the motion of the earth through the ether, if any, was too small to measure.
     
  4. Sep 28, 2010 #3

    ghwellsjr

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    I guess I should have asked a more detailed question. Let me provide some more background and try to get at what I am looking for.

    Maxwell's idea was to measure the one-way speed of light at two different times, one when the earth was moving toward to Jupiter and six months later when the earth was moving away from Jupiter. MMX measured the difference in the speed of light between two round-trip paths at the same time but in two different directions 90 degrees apart. Their experiment was actually practicable and I fully understand it but I'm not sure Maxwell's was because I don't fully understand what he was proposing.

    I think maybe what Maxwell was proposing basically amounted to observing a distant clock and measuring the time interval between "ticks" of that clock when moving toward it and then when moving away from it and calculating the speed of light, knowing the distance that the light traveled in both cases, taking the difference. But I don't know how he could know the distance accurately enough to draw any conclusion and I don't know if this would even work in principle.

    So maybe his idea was that he would have a stable clock on earth and what he wanted to measure was the "drift" in the tick rate the distant clock as the earth moved toward it and then away from it.

    So what I'm looking for is a detailed explanation of what he was proposing to measure and what he was hoping to conclude and if his experiment could have measured something that would have lead him to a false conclusion, again assuming that he had even more precise instruments than we have today.
     
  5. Sep 28, 2010 #4

    jtbell

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    Recall that Römer first calculated (an estimate of) the speed of light by comparing the timing of Jupiter's eclipses when the line of sight from the earth to Jupiter is across the earth's orbit (i.e. when Jupiter and the earth are more or less "furthest" from each other), versus when the line of sight is in the opposite direction (i.e. when Jupiter and the earth are more or less "closest" to each other).

    I suspect that Maxwell's suggestion meant to repeat this procedure twice, with lines of sight at right angles to each other. This would (hypothetically) give different speeds of light for the two directions, relative to the solar system.
     
  6. Sep 28, 2010 #5

    ghwellsjr

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    Thanks for the reply. However, see this article:

    http://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_of_the_speed_of_light" [Broken]

    If I understand it correctly, the observations of Jupiter's moon can only be done near the the 90 degree points already, in other words, as per your second suggestion (at right angles to the first suggestion) and it was no where near accurate enough for Maxwell to have used Römer's data.

    But you bring up a good point: was Maxwell simply proposing to repeat Römer's experiment with greater accuracy or did he want to do something different?
     
    Last edited by a moderator: May 4, 2017
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