Specifically, during the moves towards Le Système international d'unités in the 18th and 19th centuries, why didn't anyone attempt to move us away from the definition of there being 24 hours in a day?
Wikipedia informed me that the name second comes from the second division of an hour. It also claims that the concept of having 24 hours in a day dates back at least 6000 years to the earliest Egyptian civilization. It also says the word second (as a measurement of time) didn't make it into English until the 1500's and couldn't be measured with any accuracy for 100 years. So by one way of looking at things, the base unit of time (or perhaps the grand-pappy unit of time) is the hour.
Is there some convenient property of 24 hours = 1 day that caused it to hold on over other units? I understand the significance of a degree being 1/360th of a circle (360 = 60 * 60 = (3 * 4 * 5)^2), and 24 is closely related to those factors, but that seems a flimsy reason. The math for converting earth's rotation to elapsed time doesn't even work out very conveniently (IMO) with these units.
I expected to find a reason in time being one of the basic properties of the universe, being immutable (in 18th century eyes) and therefore used as a pivot point for other unit definitions. But the dependency graph of SI units mostly dispelled me of that: both temperature and mass were found to be as independent as time, and both units were redefined during this period (to Kelvins and kilograms, respectively).
During the same period, other units were attempted to be re-measured from new standards:
- Length was adopted to use the meter at one ten-millionth from the North Pole to the Equator in 1793
- Mass was adopted to use the gram at the cube of the hundredth part of the metre (at STP) in 1795
- Temperature was adopted to use degrees Celsius, one hundredth of the separation between boiling and freezing of water.
And yet, efforts to define the second seem to center on more perfectly measuring the existing definition of 1/86,400th of the Earth's rotation. Given the predilection for base 10 (and the gradual move away from units depending on our earthly frame of reference), why was the second left at such a cumbersome, ancient interval? Why didn't we redefine a new measure of time to be (say) 1/100,000th of a day, put 10 hours in a day, etc. etc.?
Did no one think to challenge the convention of 24 hours in a day? Why not?
That came out a little more jumbled than it was in my head, so let me sum up: I'm mainly interested in answers addressing attempts to redefine units of time and why they didn't achieve wide adoption in the scientific community.