Chapter 11 of The Idea Factory by Jon Gertner (a book about Bell Labs) has a fun story about the first transatlantic telephone cable, completed in 1956. According to him, telegraph cables were attempted as early as the 1850s, but the first successful one was in 1866, between Canada and Ireland.

I'm surprised at how many cables crossed the Atlantic in 1901. Anyone know how they power the amplifiers under the ocean? (Then and now?).

Edit: It appears that there's a separate wire carrying electricity. I'm no electrician but I was under the impression that power loses it's Voltage (or Amperage?) over distance.

See https://en.wikipedia.org/wiki/Submarine_communications_cable... for a brief overview.

Early submarine cables were literally just wires. To overcome the electrical resistance of a long cable, they simply applied a large voltage on one end, and used sensitive instruments to pick up the tiny signal on the other end.

Interestingly, the early engineers didn't fully understand how the electromagnetic properties of a cable (capacitance and inductance) affect signal propagation over long distances. So they ended up seeing unexpected amounts of distortion that forced them to transmit much more slowly than desired. The theoretical breakthrough that enabled reliably sending signals from one side of an ocean to another was thanks to Oliver Heaviside, who was pretty much the archetype of a misunderstood crackpot/genius.

But yeah, later cables included in-line repeaters, once the technology was sufficiently well developed. Here's a description of some early vacuum-tube amplifiers that were designed for extreme reliability: http://www.ase-museoedelpro.org/Museo_Edelpro/Catalogo/tubes...

Power does diminish with distance due to I2R losses. For cables using AC, there are also reactive losses. To compensate, the cable companies boost the voltage at both ends (30-500 kV) of the cable such that the repeater at the middle of the span has enough juice to operate properly. And, yes, separate cables, or wire bundles, carry the power and ground.

There's a lot more in the Pacific nowadays than on that map. And I don't think less cables are active. Our need for bandwdith nowadays compared to 1900 is much higher, a lot of those cables have simply been upgraded from carrying telegraph signals to snappy fibre optics.

What is the island(?) in the middle of the Atlantic where 5 cables meet? I can't quite make it out from the image.

The Azores?

The Azores