The Telephone: A Unit Study

The telephone as we know it is almost nothing like it was when it first appeared. To be sure, the basic principle of producing and sending sound is the same, but many improvements and solutions have been worked out since the early days.

The First Telephone

The first telephone was invented by Alexander Graham Bell in 1875. This telephone was a primitive device, consisting of a diaphragm which vibrated to sound waves, a magnet, and a coil of wires. As the diaphragm vibrated, it moved the magnet which was near the large coil of wires. Accordingly, an identical reproduction of the sound was inducted into the coil. By running the current through another device of the same type, the sound could again be created — even at a long distance from its origin. In 1877 Bell improved the telephone further by putting it into a box with a mouthpiece to talk in — or, as was really the case, shout in. The new design was rather bulky and limited in its abilities, so a team of professors quickly modified it further, increasing its efficiency and reducing its size. However it continued to be a primitive looking device.

Edison’s Telephone

But the telephone was yet to be improved. As the telephone could, of course, compete with the telegraphy that was in standard use at that time, a telegraph company hired the famous inventor of the incandescent light bulb, Thomas A. Edison, to make a telephone that wasn’t covered by Bell’s patents. That Edison did, and in short order he made a telephone that ran battery power through carbon. As Bell’s telephone used magnetic induction instead of carbon, the telegraph company wouldn’t have to pay Bell for his work. The new carbon phone worked because carbon changes its resistance and hence the flow of current through it when under pressure. Thus, Edison had made a workable telephone much more efficient than Bell’s as a greater change in current could thus be produced yielding increased volume.

The Telephone Switchboard

Making a working telephone was only half of the battle. How to make a workable telephonic system was also a challenge. To manage the incoming and outgoing messages, the original solution was to man a large switchboard with operators who were signaled to connect the appropriate lines and in turn signal the person receiving the telephone call. Unfortunately, until the advent of an improved system, when signaling the receiver of the call, everybody’s phone would ring. Each person, therefore, would count the rings, and if it was the right number of rings, he or she would pick up the receiver. Often times more than one person would pick up, so any number of ears could be listening to a conversation. Since the operators could be slow and make mistakes, a dissatisfied telephone owner designed an automatic switch to connect the appropriate lines. Today, operators have been entirely replaced with automatic circuits.

The Telephone Network

Yet another problem to be resolved was the transmission lines. As more people became attached to the system, the phone lines would have to cover a longer distance, leading to serious signal loss. It wasn’t until an improvement of Lee De Forest’s triode (three element vacuum tube capable of amplifying — the predecessor of today’s transistors) was introduced into the system in 1913 that signals could be increased within reasonable distortion levels. A few years later, with the aid of a triode oscillator, several messages were sent on the same line by simply putting them at different frequencies. Later, a more efficient system of coaxial cables and lines came into place employing microwave frequencies. But even that was to become obsolete when wireless transmitters were developed, first using microwave frequencies, and then using today’s satellites.

Even though the telephone has immensely improved since its beginnings, the general design is basically the same as the one that Alexander Graham Bell dreamed up. However, the telephone systems have vastly improved and are almost nothing like the primitive telephone on which Alexander Graham Bell transmitted his famous words, “Mr. Watson, come here, I want you,” on March 10, 1876.

Further Investigation

The First Telephone
Information from the Library of Congress for kids site.

Telephone History Timeline
From AT&T.

The First Telephone
Photo gallery of the first telephone and those following. Be sure to click on the more detailed photos.

Bell’s First Patent
Full text.

Timeline of Alexander Graham Bell
From the Library of Congress.

Alexander Graham Bell
Biography from MIT.

Activities

Bell’s Path to the Telephone
Interactive timeline from the Institute of Advanced Technology of electronic progress leading to the invention of the telephone.

String Telephone
Experiment at TeachEngineering.org to demonstrate how early telephones worked.

Alexander Graham Bell Activity Book
48-page download.

Books

History of the Telephone by Herbert Newton Casson
Free eBook that provides extensive but interesting coverage.

Great Inventors and Their Inventions by Frank Bachman
This popular free eBook contains a 19-page chapter titled “Alexander Graham Bell and the Invention of the Telephone.”

Unit Studies & Lesson Plans

Unit Study: Lines of Communication
Research and activities covering Bible, science, language arts, social studies, math, art, health, and music. (Please note, Bell’s quote to Watson and his successful experiment has apparently been given an incorrect date.)

The History of the Telephone
Teacher lesson plan that explores how telephones have changed over time.

The History of the Telephone
Student version.

Free Science Studies: Alexander Graham Bell & the Telephone
Part of our free science studies using Great Inventors and Their Inventions mentioned above includes suggestions that go with the book, and many other resources not listed here.