Code_ The Hidden Language of Computer Hardware and Software - Charles Petzold [18]
If you take an iron bar, wrap it with a couple hundred turns of thin wire, and then run a current through the wire, the iron bar becomes a magnet. It then attracts other pieces of iron and steel. (There's enough thin wire in the electromagnet to create a resistance great enough to prevent the electromagnet from constituting a short circuit.) Remove the current, and the iron bar loses its magnetism:
The electromagnet is the foundation of the telegraph. Turning the switch on and off at one end causes the electromagnet to do something at the other end.
Morse's first telegraphs were actually more complex than the ones that later evolved. Morse felt that a telegraph system should actually write something on paper, or as computer users would later phrase it, "produce a hard copy." This wouldn't necessarily be words, of course, because that would be too complex. But something should be written on paper, whether it be squiggles or dots and dashes. Notice that Morse was stuck in a paradigm that required paper and reading, much like Valentin Haüy's notion that books for the blind should use raised letters of the alphabet.
Although Samuel Morse notified the patent office in 1836 that he had invented a successful telegraph, it wasn't until 1843 that he was able to persuade Congress to fund a public demonstration of the device. The historic day was May 24, 1844, when a telegraph line rigged between Washington, D.C., and Baltimore, Maryland, successfully carried the biblical message: "What hath God wrought!"
The traditional telegraph "key" used for sending messages looked something like this:
Despite the fancy appearance, this was just a switch designed for maximum speed. The most comfortable way to use the key for long periods of time was to hold the handle between thumb, forefinger, and middle finger, and tap it up and down. Holding the key down for a short period of time produced a Morse code dot. Holding it down longer produced a Morse code dash.
At the other end of the wire was a receiver that was basically an electromagnet pulling a metal lever. Originally, the electromagnet controlled a pen. While a mechanism using a wound-up spring slowly pulled a roll of paper through the gadget, an attached pen bounced up and down and drew dots and dashes on the paper. A person who could read Morse code would then transcribe the dots and dashes into letters and words.
Of course, we humans are a lazy species, and telegraph operators soon discovered that they could transcribe the code simply by listening to the pen bounce up and down. The pen mechanism was eventually eliminated in favor of the traditional telegraph "sounder," which looked something like this:
When the telegraph key was pressed, the electromagnet in the sounder pulled the movable bar down and it made a "click" noise. When the key was released, the bar sprang back to its normal position, making a "clack" noise. A fast "click-clack" was a dot; a slower "click…clack" was a dash.
The key, the sounder, a battery, and some wires can be connected just like the lightbulb telegraph in the preceding chapter:
As we discovered, you don't need two wires connecting the two telegraph stations. One wire will suffice if the earth provides the other half of the circuit.
As we did in the previous chapter, we can replace the battery connected to the ground with a capital V. So the complete one-way setup looks something like this:
Two-way communication simply requires another key and sender. This is similar to what we did in the preceding chapter.
The invention of the telegraph truly marks the beginning of modern communication. For the first time, people were able to communicate further than the eye could see or the ear could hear and faster than a horse could gallop. That this invention used a binary code is all the more intriguing. In later forms of electrical and wireless communication, including the