This title may be a little misleading. I’ve been working on the medieval Gaelic calculations of time for a paper I am preparing on numeracy in ancient Ireland. Often information on this stuff is preserved in strange places, like stories of battles. The story Cath Maigh Rath (‘The Battle of Magh Rath’ or ‘Moyra’ as it is sometimes modernized) has a particularly detailed account of how days, hours etc. are broken down, but it is all done by relative proportions (this is two thirds of that which is one and a half of this which is …). To aid my understanding I threw together the accompanying diagram. Here below, then is a list of how it all works:
Acording to the ‘Batle of Magh Rath’, the day is divided into twenty-four hours, as is ours, but it is also divded into four quarters of six hours apiece. It gets much more complex from there. Each hour is then divided into four points (15 modern minutes) and each point is divided then into five periods that are subsequently divided into different units: 2 minutes (each = 6 modern minutes), 3 parts (each = 4 modern minutes) and five brathas (144 seconds each or 2.4 minutes). Each bratha is then comprised of one and a half ostents (96 modern seconds), but that then implies that there are 37.5 ostents in one hour. If that seems really bizarre, just remember that there are then 75 ostents in 2 hours and so on up to an even 1200 in one day.
That the five dominant periods are given no name possibly suggests that the commonly understood division of the hour was into five sections and that such did not need mention – or that it was a secret. The information in the text is given below. You have to work through the calculations to figure out that the five-fold division is the basic organizing structure.
376 atoms = ostent
1 ½ ostent = 1 bratha
1 2/3 bratha = pars
1 ½ part = minute
2 ½ minutes = point
4 points = hour
6 hours = quarter
The figure should be read as follows: The outermost ring is divided into quarters. The blue ring indicates gaelic minutes, while the green ring indicates parts. The lighter, variegated ring removed once from the middle are brathas while the innermost, brown ring represents ostent s- the half-ostent being marked with red.