I shall adopt the decimal division of the right angle, and of the day, and shall refer the linear measures to the length of the metre, determined by the arc of the terrestrial meridian comprised between Dunkirk and Barcelona.I thought that I might find a description of decimal time, or at least examples of how decimal times were written in France during the Revolution, something like 10h98m76s. However, the few examples I found look like this one:
... et la distance périhélie, égale à 1,053095 ; ce qui a donné pour l'instant du passage au périhélie, sept.29j,10239, temps moyen compté de minuit à Paris.Roughly translated, this says:
Les valeurs précédentes de a, b, h, l, relatives à trois observations, ont donné la distance périhélie égale à 1,053650; et pour l'instant du passage, sept.29j,04587; ce qui diffère peu des résultats fondés sur cinq observations.
...and the perihelion distance, equal to 1.053095, which gave for the moment of perihelion passage, Sept. 29d.10239, mean time counted from midnight in Paris.Note that the superscript "j" stands for jour, meaning "day", and that the French use a comma as the decimal mark. So Laplace is expressing the decimal time as a decimal fraction of a day in Paris mean time and adding it to the date. This is how times are given in astronomical circulars today, except that now the times are UT, and the unit symbol is omitted. So ,10239 would correspond to 1h2m39s decimal time, and ,04587 to 10h45m87s, or 1:06:03 a.m.
The previous values of a, b, h, l, relative to three observations, gave the perihelion distance equal to 1.053650, and for the moment of passage, Sept. 29d.04587; which differs slightly from the results based on five observations.
He also gives times without dates, such as 0j,681798, which Bowditch renders as 0day,681798. This is essentially identical to how Herschel wrote them a half-century later, e.g. 0d·286003.