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An hour has been divided in sixty minutes since medieval times. During the 16th and 17th century, clocks measuring a second subdivision emerged. Today we still use the sexagesimal system for dividing hours into minutes and seconds, but below that we use the decimal system (and the second is the only SI unit for time). Wikipedia notes that:

For even further refinement, the term "third" ( 1⁄60 of a second) remains in some languages, for example Polish (tercja) and Turkish (salise), although most modern usage subdivides seconds by using decimals.

The choice of the word remains leave open the possibility that there was such a subdivision in the past.

Has the English Language ever had a sexagesimal subdivision of the second?

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Right after your quote Wikipedia has

"In 1267, the medieval scientist Roger Bacon, writing in Latin, defined the division of time between full moons as a number of hours, minutes, seconds, thirds, and fourths (horae, minuta, secunda, tertia, and quarta) after noon on specified calendar dates".

This use was retained in astronomy but not colloquially, Moxon's Tutor to Astronomy and Geography. Or, An Easie and Speedy Way to Know the Use of Both the Globes (1698):

"Hours are vulgarly divided into halves, quarters and half quarters, but mathematically into minutes, seconds, thirds, fourths, etc."

Arithmetical tables in the second edition of Rusher's English Spelling Book (1851) also list a third as 1/60 of a second.

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  • $\begingroup$ Bacons hours, minutes, seconds are very different from ours so I don't think his thirds can count as a subdivision of what we know understand to be a second. I don't know his exact definition but they appear to add up to a month, rather than a day? Perhaps I misunderstand what is being said here. $\endgroup$
    – gerrit
    Commented Mar 28, 2017 at 17:58
  • $\begingroup$ @gerrit Bacon broke with Ptolemy and Grosseteste, who subdivided a day into 60 minutes, and subdivided an hour into 60 minutes. His hours certainly did not add up to a month since in Compotus he computes the grand cycle as "344 calendar years, plus 361 days and 1 hour", see Astronomies and Cultures in Early Medieval Europe. $\endgroup$
    – Conifold
    Commented Mar 28, 2017 at 18:42
  • $\begingroup$ This answer is wrong. The division of hours into 60 minutes, minutes into 60 seconds, seconds into 60 "thirds", and so forth is commonplace in Arabic-speaking astronomers from at least the 9th century onwards, long before Bacon. $\endgroup$
    – fdb
    Commented Mar 29, 2017 at 17:11
  • $\begingroup$ Also, Ptolemy did divide the day into sexagesimal fractions, but he did not refer to sixtieths of a day as “minutes”. $\endgroup$
    – fdb
    Commented Mar 29, 2017 at 17:17
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    $\begingroup$ @fdb The question is about the use of thirds in English. I did not even claim that Bacon was first to introduce them there, let alone first to introduce sexagesimal subdivisions altogether. The source on Ptolemy and Grosseteste is Thorndike's History (p.124), but it is dated. Do you have more recent references? $\endgroup$
    – Conifold
    Commented Mar 29, 2017 at 18:21
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Oxford English Dictionary
third, adj. (and adv.) and n.
Definition B.7.a.

The third of the subdivisions of any standard measure or dimension which is successively subdivided in a constant ratio; the subdivision next below seconds: see prime n.2 2 ...

with some quotes

1595 J. Davis Seamans Secrets i. sig. B4, Euery degree..doth containe 60 minutes, and euery minute 60 seconds, and euery second 60 thirds, &c.

1694 W. Holder Disc. Time ii. 32 To divide..an Hour into 60′ (Minutes), a Minute into 60″ (Second Minutes), a Second Minute into 60‴ (Thirds).

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  • $\begingroup$ What is the date of publication of this dictionary? It makes no note of out of date? $\endgroup$
    – gerrit
    Commented Mar 30, 2017 at 12:54
  • $\begingroup$ @gerrit ... It is the on-line version of the OED ... this entry says First published in 1912, and at the bottom lists some Draft additions of September 2016. No: Definition 7.a. is not marked as absolete, although 7.b. just below is. $\endgroup$
    – Gerald Edgar
    Commented Mar 30, 2017 at 12:57

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