"The average person in Hellenic and Roman times knew that our world is round. ... Pythagoras was probably the first to assert that Earth is a
sphere. The other candidate for originating this insight is Parmenides of Elea. ... Aristotle notes the reasons offered by Anaxagoras and Democritus for asserting that Earth is flat. Then he argues against them, and states: "These conditions will be provided, even though the Earth is spherical, if it is of the requisite size..."
... Eratosthenes of Cyrene measured the circumference of the Earth by comparing shadows on the first day of Summer. ... The earliest coins that have
terrestrial globes on them are from Uranopolis ("Sky City") in Macedonia, which was founded on Mt. Athos about 300 BCE by Alexarchos, brother of the king Kassander. ... A coin of Roman imperial times (BMC 125) shows Commodus on the obverse. On the reverse, a man stands facing right, naked to the waist, holding a globe. ... Struck during the reign of Trajan, a coin from Samos honors Pythagoras (BMC Ionia Samos 237). The reverse shows Pythagoras
touching a globe with a wand. This same theme appeared on coins struck for Septimus Severus, Julia Mamaea, Trajan Decius, and Etruscilla. ...
Once I started looking for globes, they became easy to find. I have a Providentia/Globe denarius from Marcus Aurelius and another from Trajan,...
https://www.answering-islam.org/Scien...

See also, one of many discussions among numismatists here:
http://www.forumancientcoins.com/boar...

Ptolemy knew the world was round in 150?!--Well, I read in some writing of Aristotle about the world's being round. So maybe the idea of its not being flat occurred earlier than Galileo's time.

Chronometers were in common use for naval navigation at least into the 1980s, but they were modern designs. Does "reinstate Harrison's longitudinal clocks for modern-day Naval use" mean the original Harrison chronometers?

Excellent story and a treasured bit of history. I learned some of that in the US Power Squadron sailing/navigation classes I had to take in order to captain our first sailing yacht the USS Carlinda.

Longitude, the movie:
An outgrowth of a 1999 BBC documentary, the two-part British miniseries Longitude goes out on a creative limb by unfolding two parallel stories, each separated from the other by some 200 years. In one of the plot lines, Michael Gambon (who won one of the series' many BAFTA awards) stars as real-life 18th century clockmaker John Harrison, whose invention of a "marine chronometer" would ultimately serve as the primary navigational guide for sailors of his era -- but not without a lot of sacrifice and frustration on Harrison's part. The second continuity takes place in the immediate post-WWI era, as Royal Navy officer (and shellshocked war veteran) Rupert Gould (Jeremy Irons) battles bureaucracy and ignorance to reinstate Harrison's longitudinal clocks for modern-day Naval use. As the action hopscotches between the two story lines, Harrison painstakingly assembles his chronometer and attempts to promote the device to the unresponsive powers-that-be, while Gould tries to carry on Harrison's work without losing his sanity in the process. Based on the book by Dava Sobel, Longitude was originally telecast over Britain's Channel 4 on January 2 and 3, 2000, then was seen in America courtesy of the A&E cable network.
https://www.rottentomatoes.com/m/long...

https://www.rottentomatoes.com/m/long...
An outgrowth of a 1999 BBC documentary, the two-part British miniseries Longitude goes out on a creative limb by unfolding two parallel stories, each separated from the other by some 200 years. In one of the plot lines, Michael Gambon (who won one of the series' many BAFTA awards) stars as real-life 18th century clockmaker John Harrison, whose invention of a "marine chronometer" would ultimately serve as the primary navigational guide for sailors of his era -- but not without a lot of sacrifice and frustration on Harrison's part. The second continuity takes place in the immediate post-WWI era, as Royal Navy officer (and shellshocked war veteran) Rupert Gould (Jeremy Irons) battles bureaucracy and ignorance to reinstate Harrison's longitudinal clocks for modern-day Naval use. As the action hopscotches between the two story lines, Harrison painstakingly assembles his chronometer and attempts to promote the device to the unresponsive powers-that-be, while Gould tries to carry on Harrison's work without losing his sanity in the process. Based on the book by Dava Sobel, Longitude was originally telecast over Britain's Channel 4 on January 2 and 3, 2000, then was seen in America courtesy of the A&E cable network.

The book was discussed on the forum here https://www.galtsgulchonline.com/post...

What is the movie you saw? A NOVA documentary in 1998 based on the book was very good. https://www.pbs.org/wgbh/nova/longitu...

I forgot about the "challenge'. Thanks.

My brother made me get a mechanical watch, since we are mechanical engineers. I am an idiot, so now I have several.

One of my favorite professors used to say that most fundamental mechanical technology came from locks, clocks and firearms.

A Turkish guy, son of a watchmaker, gave me the book a while ago. https://www.amazon.com/Longitude-Geni...

Watches are cool!

Right.
The invention of that accurate clock was prompted by a big money prize to be awarded by the Royal Society (of Science).
After testing and observing, finding it did what they asked for, they procrastinated. I cannot recall if Harrison ever got the money as promised.

I highly recommend the movie Longitude.
It is not a fast moving adventure film, but it highlights the efforts of John Harrison, and the stupidity of the British state that continually interfered with his work and favored the less than rational attempts by looters with pull.

I think the movie was recommended to me by someone here in the Gulch several years ago.
Another of many reasons that I am glad to be here. ;^)