The telephone came about as scientists tried to squeeze more out of the telegraph. They began to understand how to influence sound, and how to send it over longer and longer distances to more and more people. Although the telephone itself hasn't really changed much in the last hundred years - and the telegraph's 'ons' and 'offs' live on in the binary codes used by today's digital technology - considerable adaption was needed to accomodate new devices like fax machines and modems.
How the telephone works
The telephone combined the knowledge of how sound works together with a variable electric signal that could be sent over great distances. Instead of the telegraph's simple electrical pulse - on or off - the telephone uses an electrical signal that changes in amplitude (volume) and frequency (pitch) across time - in other words, a 'continuously varying signal'. This is more like real life, and means that the telephone is able to carry a human voice. But for the scientists of the day it required a better understanding of electricity as well as technological progress in the areas of cables and switches.
The telephone combined the knowledge of how sound works together with a variable electric signal that could be sent over great distances. Instead of the telegraph's simple electrical pulse - on or off - the telephone uses an electrical signal that changes in amplitude (volume) and frequency (pitch) across time - in other words, a 'continuously varying signal'. This is more like real life, and means that the telephone is able to carry a human voice. But for the scientists of the day it required a better understanding of electricity as well as technological progress in the areas of cables and switches.
Sound : good vibrations
The sound waves that you hear are quite simply movements or vibrations of air. These sound waves travel through air, like the wind, by changes in air pressure.
Different sounds come about because the air vibrates at different frequencies. And as the trailer for the film 'Alien' made clear - 'in space, no-one can hear you scream ...' - sound can't travel in a vacuum because there's no air.
The substance that a sound wave travels through is called its 'transmission medium'. Sound waves can, in fact, travel through almost any medium, such as water or the bricks in your house, and in many cases much further than in air. Whale songs can travel for hundreds of miles underwater, although you'd need special equipment to listen to them if you were more than about 10 miles away.
The sound waves that you hear are quite simply movements or vibrations of air. These sound waves travel through air, like the wind, by changes in air pressure.
Different sounds come about because the air vibrates at different frequencies. And as the trailer for the film 'Alien' made clear - 'in space, no-one can hear you scream ...' - sound can't travel in a vacuum because there's no air.
The substance that a sound wave travels through is called its 'transmission medium'. Sound waves can, in fact, travel through almost any medium, such as water or the bricks in your house, and in many cases much further than in air. Whale songs can travel for hundreds of miles underwater, although you'd need special equipment to listen to them if you were more than about 10 miles away.
Copper cables
Cables and wires are the unsung heroes or 'facilitators' of the age of telecommunication. In the space of twenty years, cables changed from two mile long wooden troughs containing copper wire in grooves to cables that could be laid underwater across the Atlantic. This required enormous technological feats. Perhaps more surprisingly, copper cables have also stood the test of time, as scientists and engineers have developed techniques to squeeze more and more out of them.
Cables and wires are the unsung heroes or 'facilitators' of the age of telecommunication. In the space of twenty years, cables changed from two mile long wooden troughs containing copper wire in grooves to cables that could be laid underwater across the Atlantic. This required enormous technological feats. Perhaps more surprisingly, copper cables have also stood the test of time, as scientists and engineers have developed techniques to squeeze more and more out of them.
Networks
The complexity of a network - telephone or computer - rises dramatically with the number of people connected to it. This was not something that had bothered people until the telephone became widespread, when it suddenly became really important. If there are only a few people with telephones, the network is quite simple and everyone can be connected to everyone else. If there are more people, you need some sort of exchange to connect a call to another person through a central system. But if there are thousands of people it gets much more complicated
The complexity of a network - telephone or computer - rises dramatically with the number of people connected to it. This was not something that had bothered people until the telephone became widespread, when it suddenly became really important. If there are only a few people with telephones, the network is quite simple and everyone can be connected to everyone else. If there are more people, you need some sort of exchange to connect a call to another person through a central system. But if there are thousands of people it gets much more complicated
Modems and Faxes
One thing that has extended the use of the telephone system is the way that new machines, like computers and faxes, have been connected to the existing network - the cables and exchanges that form the telephone infrastructure. To take advantage of this infrastructure, the machines are designed to work with the existing system. This means that the signals have to be in a range that the telephone wire can handle. As the telephone is designed to carry speech, you can hear strange whistling sounds coming out of modems and fax machines - they are communicating with each other in the range of the human ear.
One thing that has extended the use of the telephone system is the way that new machines, like computers and faxes, have been connected to the existing network - the cables and exchanges that form the telephone infrastructure. To take advantage of this infrastructure, the machines are designed to work with the existing system. This means that the signals have to be in a range that the telephone wire can handle. As the telephone is designed to carry speech, you can hear strange whistling sounds coming out of modems and fax machines - they are communicating with each other in the range of the human ear.
