No. This is not as simple as you think. The line has resistance, capacitance and inductance. Early lines were of very poor quality.
Even with high quality modern transmission lines, resistive losses are minimised but the line has capacitance and inductance.
1958?
books.google.com has a copy of George B. Prescott’s 1860 classic History, Theory and Practice of the Electric Telegraph. Chapter 14, “The Atlantic Cable”, starting on page 179, discusses the 1858 cable, and the struggles they had getting any messages across during its short life. This book was published before the successful 1866 cable was laid, so much of this chapter is spent refuting claims that the whole thing was a hoax.
I just watched a video about this so I signed up to post what it says about this. hammos1’s reply is the best answer. If anybody is interested in watching a three hour video on the history of electricity they explain it in more detail:
But to paraphrase the video, the message they wanted to send was only 98 words long, but the message was garbled so they had to repeat the message several times, so what was actually sent was much more than 98 words one way. They didn’t fully understand how electricity worked in communication lines when they built the first cable…that was the problem, and the reason why the messages were garbled. Some engineers later figured out the math and used that to build the replacement cable with better specifications.
According to that video, I’m not sure if it “broke down” or was accidentally destroyed. One engineer thought the way to solve the signal problem was to increase the voltage (which at the time might have seemed logical but we now know it was the wrong thing to do). It sounds like what may have happened is he “fried” the cable with too much voltage.
Ahh, okay. At first I figured you posted this via transatlantic telegraph back in '09.
I don’t understand. I picture an electric wire with insulator like, in cross-section, a point–the wire, some space, then a circle surrounding the point–the insulator.
If only the wire is doing the heavy lifting, why does the insulator matter?
The wire isn’t a (perfect) conductor, instead it’s a long resistor. And the cable acts like a long string of capacitors in parallel, each separated by the resistor. If you connect a battery across the cable-pair at one end, the voltage at the other end rises slooooooolwy. In other words, any sharp-edged dots and dashes will become totally distorted: their higher frequencies are filtered out, and different lower frequencies travel at different speeds along the cable.
The same effects made long-distance telephone communication impossible.
Oliver Heaviside solved the problem theoretically in 1887, see Loading coil - Wikipedia
A long-but-very-interesting article here about the history of undersea cable communication. According to the article, the voltage was eventually turned up so high that it arced through the insulation, creating a conductive path between the wire core and the surrounding sea water. The wire core itself wasn’t compromised, but that arc through the insulation created a short-circuit to ground, so that now no matter how much voltage they applied at one end, no current (and hence no signal) could be made to reach the receiver on the far end of the cable.
You beat me to linking that article. And I’ve only had 3.5 years!
An important point assumed but not pointed out above is that it’s not just one wire that matters, but the pair of wires. Between the two wires there is a capacitance. I don’t know the details, but my guess is that the two main factors are the resistance of the wire and the capacitance of the space between the two wires. I further suspect that the capacitance is related to the type of insulation between them as well as the distance between them.
I don’t know whether the insulation around the pair matters; if it does I’d like to hear more about that.
BTW on a recent thread here someone who knows more than I do about this stuff also claimed that .6c is typical for long distance optical transmission.
Because the wire-insulator combination creates a capacitor (a capacitor is created when two conductors are separated by an insulator - in this case, the other conductor is the shield, or just the surrounding seawater).
And, as pointed out above, very long cables can have very high resistance and capacitance, which tends to mess up the signal integrity.
There’s a lot of information about that here.
Not two wires - it’s between one wire and the surrounding seawater/grounding. As current flows, it induces magnetic fields which induce current in turn - thus as mentioned above, applying an instantaneous rise in voltage at one end does not create an instantaneous rise at the other end.
A square wave (instant on, instant off) is actually a sum of various harmonics of sine waves. As a resultof capacitance and inductance, the effect is as if each frequency of sine wave travels at a different speed. the signal is “smeared”.
As mentioned in the Wired article, the intial bull-headed engineer solution was to turn up the voltage. That did not change the fundamental physics.
But does an electrical signal actually travel along a conductor at the speed of light?
I remember reading that, while individual electrons move at the speed of light, they moved in all sorts of directions, but the sum of their movement was along the conductor. The actual speed of the signal along the conductor was thus determined more by factors like voltage, resistance and the conductors characteristics than the local speed of light.
Not even fiberoptic cables carry signals at the speed of light (the actual light beam bounces from side to side along the cable, travelling a distance far greater than the actual length of the cable).
No, as stated above, signals in coaxial cables move at much less than the speed of light, usually 70-90% of c.
Also, the individual electrons move very, very slowly. It’s the Electrical Field that travels quickly.
That means the electrons move as a result of the electrical field, rather than generating it by their movement, correct? or are there some weird physics going on that allow the field to move faster than the objects affecting it? They’re both equally mind-bending.
You’ve slightly underestimated the length of Victorian words. Here’s the full text of the first cable (fromhere):
I count (well Word did it for me) 521 characters without spaces, 619 with. Giving a transmission rate of 36 characters per hour (including spaces).
Wow. It must have been quite amazing at the time to be able to communicate with someone across the ocean in a single day. But I didn’t realize just how slow the first cable was (although I’m not really surprised now that I think about it). The ping time may have been much faster, but the bandwidth would have been orders of magnitude lower than just transporting a bunch of letters by ship!
The then holder of the Blue Riband the Persia made the crossing in 9 days, 16 hours and 6 minutes (232 hours). She had a gross registered tonnage of 3,300 tonnes, so could carry maybe 1,000 tonnes of cargo?
In 232 hours the cable could have transmitted 8,352 characters - one decent sized Victorian epistle or so. So for bulk data transfer the ship smoked the cable.
Still have things really changed that much. How much data can you fit onto a 747 laden with USB drives?
Just for fun:
747-ERF can carry 248,000 pounds of cargo. Looks like hard drives are up to 4 terabytes each now, and a 3.5" SATA drive weighs in at about 1.6 pounds. So that’s 155,000 hard drives, for 620,000 petabytes of data.
Flight time from Dulles to Heathrow is 7hrs 15min. So bandwidth is…
23.8 terabytes per second.
In the 9+ days it would have taken the Persia to make the crossing, the 747 could have made 15 round trips, moving 1860 tons of cargo in each direction. Double the time (so the Persia can make a round trip and move 1000 tons of cargo in each direction), and the 747 wins by a factor of 3+.
Awesome, 23.8 terabytes per second is a lot faster than any current transatlantic links we have now isn’t it?