Undersea Cables

Q. If a cable company put down a cable its length would have to be longer than predicted (by round earth geometry) if the world were flat. If somebody put down a bunch of cables and found that they were longer than they'd expected, wouldn't they tell somebody?

A. But the cables are always longer than expected. It's just explained by underwater currents, soil irregularity, winds and errors in placement, et cetera. And somewhere in that is lost a mistake caused by a slight misunderstanding of the Earth's shape.

The Transatlantic Cable

In the book "The Laying of the Cable" by John Mullaly we read journal entries showing that segments between various points on the supposed globular earth required surplus cable.

In the following entry 16% surplus cable is reported:

"Total amount of cable paid out, 949 miles 660 fathoms; total amount run by observation, 818 miles; total amount run by patent log, 802 4-10 miles; total amount run by ship's log, 810 1/4 miles; total amount run by engineer's log, 815 1/3 miles. Surplus cable paid out over distance run by observation, 131 miles 660 fathoms, about 16 percent.; 64 miles from the Telegraph House. Received signal from Agamemnon at noon that they had paid out from her 940 miles of cable. Passed this morning several icebergs. Made the land off entrance to Trinity Bay at 8 P.M. Entered Trinity Bay at 12 30 P.M. At 2 30 P.M. stopped sending signals to Agamemnon for 14 minutes, for the purpose of making splice. —"The Laying of the Cable," John Mullaly

Another segment of the cable laying showed a 15% surplus:

"Thursday, August 5.—At 145 A. M., Niagara anchored. Distance run since noon yesterday, 64 miles; amount of cable paid out, 66 miles 382 fathoms, being a loss of less than 4 per cent. Total amount of cable payed out since splice was made, 1,016 miles 600 fathoms. Total amount of distance, 882 miles. Amount of cable paid out over distance run, 134 miles 600 fathoms, being a surplus of about 15 percent. At 2 A. M. I went ashore in a small boat, and awoke persons in charge of the Telegraph House, half a mile from landing, and informed them that the Telegraph fleet had arrived, and were ready to land the end of the cable. At 2 45 received signal from the Agamemnon that she had paid out 1,010 miles cable. —"The Laying of the Cable," John Mullaly

Additional quotes similar to the ones above may be found in the work as well.

Southern Hemisphere Cables

Of interest, there are relatively few submarine cables which travel East-West in the Southern Hemisphere.

https://www.submarinecablemap.com/