I had heard that of the ancient Greeks, though Wikipedia gives the origin more vaguely as the ancient Near East. It is a practical way of thinking when you are outdoors most of the time, you are not very active at night, and a sundial is your timekeeper. It also helps to be at a relatively low latitude, where the seasonal variation is not so great.
This makes sunrise and sunset the important moments in daily timekeeping, and this is, of course, the case in the Jewish definition of a day (I would not be surprised to learn that Jewish scholars also worked with intraday fractions of the lunar cycle.)
If this did lead to a willingness to vary the second along with the length of the hour, this would seem to me to argue against the specialness of the definition of the second as 1/86400 of the mean synodic day. I doubt, however, that anyone but perhaps a few scholars at that time ever contemplated such a small division of time. The second only became a practical measure with the development of accurate mechanical clocks, by by then, mean time had largely taken over sundials and other forms of intraday ephemeris timekeeping, as that is what mechanical clocks measure. (This transition, I suspect, had a greater impact on the general population than did the adoption of the atomic standard, if only because the latter had no practical impact.) At that point, the second was defined by sexagisimal division of the hour (and thus, obviously, transitively as a fraction of a particular mean synodic day, given the definition of an hour in such terms.)
I had heard that of the ancient Greeks, though Wikipedia gives the origin more vaguely as the ancient Near East. It is a practical way of thinking when you are outdoors most of the time, you are not very active at night, and a sundial is your timekeeper. It also helps to be at a relatively low latitude, where the seasonal variation is not so great.
This makes sunrise and sunset the important moments in daily timekeeping, and this is, of course, the case in the Jewish definition of a day (I would not be surprised to learn that Jewish scholars also worked with intraday fractions of the lunar cycle.)
If this did lead to a willingness to vary the second along with the length of the hour, this would seem to me to argue against the specialness of the definition of the second as 1/86400 of the mean synodic day. I doubt, however, that anyone but perhaps a few scholars at that time ever contemplated such a small division of time. The second only became a practical measure with the development of accurate mechanical clocks, by by then, mean time had largely taken over sundials and other forms of intraday ephemeris timekeeping, as that is what mechanical clocks measure. (This transition, I suspect, had a greater impact on the general population than did the adoption of the atomic standard, if only because the latter had no practical impact.) At that point, the second was defined by sexagisimal division of the hour (and thus, obviously, transitively as a fraction of a particular mean synodic day, given the definition of an hour in such terms.)
https://en.wikipedia.org/wiki/Hour https://en.wikipedia.org/wiki/Second#History_of_definition