Abstract
ROMER'S DISCOVERY OF THE VELOCITY OF LIGHT (“Om Ole Rømers Opdagelse of Lysets Tøven”: Høst & Søn, København).—When Romer in 1676 announced to the Paris Academy his discovery of the gradual propagation of light from observations of the first satellite of Jupiter in the course of eight years, he gave no details as to these observations. He merely stated that the period of revolution of the satellite deduced from immersions in the shadow of Jupiter (when the earth is approaching Jupiter) was always shorter than the period found from emersions observed when the earth was receding from the planet. The result was that light took about twenty-two minutes to travel over the diameter of the earth's orbit. (It appears from a letter to Huygens that this was found from observations made in 1671–73.) The only observation quoted in the short paper was one of an emersion on November 9, 1676, at 5h. 35m. 45s. p.m., ten minutes later than was calculated from observations in the previous August, as predicted by Romer in the beginning of September. Three years ago a sheet was found in the University Library at Copenhagen on which was written in Römer's hand a list of eclipses of the satellites observed in the years 1668—77. In a PaPer published in the Transactions of the Danish Academy of Sciences Mrs. Kirstine Meyer discusses these observations in order to find whether they represent a part of the material on which Romer's discovery was based, and shows that this is really the case. It is shown by several examples that the observations of 1671–73 give, in fact, the approximate result announced by Romer, but that the single results differ a good deal. It is interesting to see from some figures jotted down by Romer in the MS. in question that among the values found by him for the time light takes to pass from the sun to the earth is also the correct one of about eight minutes, but he probably rejected this result as founded on rather short intervals of time. The author calculates the amount resulting from the published observation of November, 1676, and finds that it is eight and a half minutes. Curiously enough, Newton, in his “Optics,” gives eight minutes, though the only result published by Romer was about eleven minutes.
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Our Astronomical Column . Nature 98, 317 (1916). https://doi.org/10.1038/098317a0
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DOI: https://doi.org/10.1038/098317a0