Talk:International System of Units/Archives/01/2020

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In the table of successive definitions of SI base units (at the end of International System of Units#Historical definitions), the absence of an "origin" abbreviation at the end of the "prior" definition of the second as the 86400th part of a day, together with the note at the bottom, "All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure." seems to mean that that definition of the second was first decided upon by either the CGPM or the CIPM. Was there really no use of the word "second" as 1/(60.60.24) of a day before 1875 (when the CGPM, which elects the CIPM, came into being)? Maybe there should be a note or a symbol on that line, mentioning that the second is the only SI base unit whose use (under its present name and its "prior" definition) goes back to long before the French revolution. My guess is "whenever constant hours came into use" but I'm not sure about that. — Tonymec (talk) 15:29, 17 January 2020 (UTC)
P.S. A similar case applies to the "centigrade scale" (predecessor of the kelvin), with date 1743 (prior to 1875) and no authority symbol (Anders Celsius?). — Tonymec (talk) 15:46, 17 January 2020 (UTC)

By 1875 mean time had displaced apparent solar time for ordinary everyday use. But there were plenty of people alive who could remember using apparent solar time for daily life, astronomy, and navigation. So a formal definition of which was to be the basis of the metric system was in order. Jc3s5h (talk) 20:05, 17 January 2020 (UTC)

That's the end of the 19th century. My question was: Wasn't the second, as 1/60 of a minute which was 1/60 of an hour which was 1/24 of a day, in use a century or more before that? And since when? (the "prior" line for the second, "1/86400 of a day of 24 hours of 60 minutes of 60 seconds", doesn't distinguish between solar time and mean time, I suppose because going from one to the other can be (IMHO rightly) regarded as a "non-significant interim change" which may be left unmentioned). Similarly, by whom was the centigrade scale defined in 1743 (more than a century before the CGPM existed, and almost half a century before the French revolution)? By Celsius as the modern name of that scale seems to imply? Or by someone else, and who? — Tonymec (talk) 21:54, 17 January 2020 (UTC)

McCarthy and Seidelmann in Chapter 12, "Definition and Role of a Second", section 12.1 "The Historical Second", state

The definition of the second was assumed to be the sixtieth part of a minute which was the sixtieth part of an hour, and nothing mor formal than that was required. Tito Livio Buranttini (1616–1681) (Buranttini, 1675) perhaps provides the first formal definition of the second as 1/86400) of a solar day (Leschuitta, 2005)....The organization responsible for world metrology surprisingly never formally defined the second of mean solar time (Andouin and Guinot, 2001).^[1]

They go on to say, in section 12.2, that the first modern formal definition was of the ephemeris second, by the CGPM in 1954. Jc3s5h (talk) 22:21, 17 January 2020 (UTC)

Thanks for the reference to Tito Livio Burattini. Am I right in assuming that the 1743 date for the centigrade scale refers to Anders Celsius? — Tonymec (talk) 07:41, 18 January 2020 (UTC)

I don't have any literature about temperature. Jc3s5h (talk) 13:14, 18 January 2020 (UTC)