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Time transfer in the late 19th c was best achieved by telegraph, a major improvement in the determination of longitude for geodetic surveying. A question was posed, to acquire a high accuracy time, by the use of telegraph, how much signal delay would be attributed to the signal propogation over telegraph lines?

How much delay would a telegraph signal have in a 900 mile telegraph time transfer?

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  • \$\begingroup\$ Can't you calculate it? The signal propagation time is roughly the speed of light. \$\endgroup\$ – Eugene Sh. Jul 18 '16 at 14:30
  • \$\begingroup\$ It's the speed of light, less a bit for dielectrics around the line, less a lot more if the link used loading coils to equalise the LR and CG ratio for low distortion signalling. \$\endgroup\$ – Neil_UK Jul 18 '16 at 14:35
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    \$\begingroup\$ "A major achievement in longitude determination in geodetic surveying." This is not a sentence. There is no verb. It makes no sense and it is not clear why you think there is a connection between telegraph and surveying. What does "time transfer" mean? Do you mean "transit time"? Please edit your question. \$\endgroup\$ – Transistor Jul 18 '16 at 16:32
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    \$\begingroup\$ The electrical delay would be negligible if the message had to go through another operator or two. \$\endgroup\$ – Andrew Morton Jul 18 '16 at 16:59
  • \$\begingroup\$ @transistor time transfer is about synchronization of clocks in the victorian age so that railway timetables made sense. Before that requirement each town and village/district calculated local time without considering others. \$\endgroup\$ – Andy aka Jul 18 '16 at 17:27
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900 miles at c is about 4.8 miliseconds. The propagation may be slightly slower; coaxial cable propagates at about 2/3 c.

This is still a consideration today; see the famous 500 mile email bug.

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  • \$\begingroup\$ The funniest thingis that on one wire there are many bits at tthe same time, like it were bubbles in a water pipe \$\endgroup\$ – Gregory Kornblum Jul 18 '16 at 15:26
  • \$\begingroup\$ Well, they're just waves; this is why the "wave propagation through a slinky" demo is good for understanding transmission lines. \$\endgroup\$ – pjc50 Jul 18 '16 at 15:29
  • \$\begingroup\$ Waves are the fronts. \$\endgroup\$ – Gregory Kornblum Jul 18 '16 at 15:36
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    \$\begingroup\$ I'm pretty sure that old telegraph lines had a propagation velocity significantly worse than 2/3 c, especially pre-Heaviside, but I'd need to do some heavy research to get any kind of numbers. I expect the delay is still small compared to the accuracy of Victorian clocks, and in any case if you have a round-trip circuit you can cancel out the delay. \$\endgroup\$ – hobbs Jul 18 '16 at 19:02
  • \$\begingroup\$ A letter from George Stokes to William Thomson (Lord Kelvin), published in the Philosophical Transactions of the Royal Society in 1855, mentions a "retardation" (propagation delay) in a 200-mile telegraph cable from London to Brussels, of 100 milliseconds:archive.org/stream/philtrans02617140/02617140#page/n12/mode/1up \$\endgroup\$ – hobbs Jul 19 '16 at 6:07

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