Talk:Fizeau's measurement of the speed of light in air

313000 or 315000?
The source cites 315000km/s as the speed obtained and not 313000 km /s as said on the article. Though both coincide in that that speed is 5% superior to c, that speed would be 314782.08(km ∕ s) as obtained with qalculate, rounded on milliards 315000 km/s. --Neurorebel (talk) 04:49, 11 June 2017 (UTC)


 * Online, one sees at least three different figures for what Fizeau supposedly measured, including 313000 km/s, 313300 km/s, and 315000 km/s. As might be expected, people copy-and-paste a lot, so the accuracies of the cited figures are questionable.
 * For the distance that light travels in one second, Fizeau wrote:
 * "La moyenné deduite des vingt-huit observations qui ont pu être faites jusqu'ici donne, pour cette valeur, 70948 lieues de 25 au degre."
 * "The mean of the twenty-eight observations which have hitherto been made, gives for this value 70948 leagues of 25 to the degree." (Google translate)
 * The French league differed over the centuries from 3.248 km to 4.678 km.
 * The particular league that Fizeau used, the "league of 25 to the degree", was linked to the circumference of the Earth, with 25 lieues making up one degree of a great circle. Wikipedia lists this league as having a length of ~4.448 km.
 * Assuming the correctness of the Wikipedia figure, I get 315576 km/s.
 * I am not 100% sure of the correctness of the Wikipedia figure for the length of the league, and for me to put the results of my calculation on the page would be WP:ORIGINAL. However, I will correct the page to 315000 km/s as representing the best published statement of Fizeau's result, as well as being in accordance with the cited reference. Stigmatella aurantiaca (talk) 06:39, 11 June 2017 (UTC)
 * thanks for the rapidness of your response, 315000 not only in concordance with the cited source but also it makes the article coherent as 313000 is 4(,4)% of the speed of light and not 5%, again im using qalculate which sppeed of light value is fixed to 299.79246(km ∕ ms).--Neurorebel (talk) 00:40, 12 June 2017 (UTC)
 * Note: A modern value of the meridonal circumference of the Earth would put the "league of 25 to the degree" as having a value of 4.453 km. However, the measurement of the league used in France apparently dated back to 1669, so it undoubtedly would not have matched the results of a modern computation. See Units of measurement in France before the French Revolution. Stigmatella aurantiaca (talk) 07:04, 11 June 2017 (UTC)

If you read Fizeau's article, the calculation is evidently 2 x 8633m x 25.2 x 720/s = 313,274,304 m/s. He gives the numbers 8633m, 25.2 and 720, however he does not give the result in m/s, he gives it in "leagues of 25 to the degree". Some people translate this back into m/s to get values such as 314,000 km/s and 315,000 km/s, but we should not use these. We should use 313,274,304 m/s, rounded to 313,000 km/s or 313,300 km/s if desired. cagliost (talk) 23:34, 9 March 2023 (UTC)

"Fizeau–Foucault apparatus" listed at Redirects for discussion
The redirect [//en.wikipedia.org/w/index.php?title=Fizeau%E2%80%93Foucault_apparatus&redirect=no Fizeau–Foucault apparatus] has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at  until a consensus is reached. Tevildo (talk) 14:44, 6 January 2024 (UTC)