The T5 “Centuries” series presents the 18th century, 1700 to 1799, for the 18th disk.
(Image: © Copyright Gregory Williams (Flickr) and licensed for reuse under Creative Commons Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0))
It’s hard to make out all the detail here. On the left side it looks like a clock or watch with two or three hands, and on the right side is a map of the world – Africa and Asia. In the bottom right corner there’s some kind of engine or pump, with smoking chimneys in the background.
The 18th century gave us steam power, the Industrial Revolution, and John Harrison:
John Harrison (1693–1776) was a self-educated English carpenter and clockmaker. He invented the marine chronometer, a long-sought after device for solving the problem of establishing the East-West position or longitude of a ship at sea, thus revolutionising and extending the possibility of safe long-distance sea travel in the Age of Sail. The problem was considered so important following the Scilly naval disaster of 1707, that the British Parliament offered financial rewards of up to £20,000 (£2.81 million) under the 1714 Longitude Act.
We can decode the symbols using our key:
The backslash and backwards question mark strongly suggest that I flip it horizontally:
e a r s ? / p l a <-
c e a n d t i m e ->
After trying various flips, I chose this:
t i n a l l t h e (flipped vertically)
giving, probably, the following text for this disk:
....t in all the ...............ears? Place and time ...............