We now direct your attention to the third display case.

These beautiful glass objects are insulators. Look at the telephone pole against the wall with the crossarm mounted near the top (pictured below). You will see insulators installed on wooden pegs to support the “open wire” strung between telephone poles.

Why are insulators so many different colors? There are several reasons. Glass companies often made insulators at the end of the day with whatever glass was left over. For instance, when the glass company finished a run of green bottles, all telephone insulators made that day would be green.

Glass insulators were very sturdy; many stayed in place for years. Over time, the color of the glass often changed after long-term exposure to the ultraviolet radiation of bright sunlight. This is why some insulators are unique colors.

Displayed in the same case are some toy telephone sets. Toy telephones have been with us since the invention of the telephone. They aren’t just fun to use—they are also important since they teach young folks how to use the telephone.

Let’s look at the business end of a telephone pole. Basic pole line construction is covered in
this 1908 booklet by Western

Each separate telephone wire was strung from pole to pole and tied to its respective insulator. Each pole has one or more wooden crossarms. Wooden pins—typically made from weather-resistant locust wood—are fitted into each crossarm. On top of each pin is a glass insulator. There are screw threads cast into the underside of the insulator so that it can screw down onto the top of the wooden pin, which is also threaded. Why is the insulator made from glass? Why does it have a special shape? And why is it necessary? Isn’t wood a “good enough” electrical insulator?

If it never rained, there might not be a need for glass insulators, although the smooth surface and high strength provides a good anchor point to support the telephone wire. But rain is the problem. Water, mixed with salts and other impurities, conducts electricity. If the wood pin supporting each insulator got wet when it rained, it would conduct electricity and thus leak electrical current from the telephone circuit. This might cause noise and loss of volume. Or it might even cause the telephone circuit to fail completely.

To avoid this, the wide skirt of the glass insulator forms an umbrella to keep the wood “pin” underneath it nice and dry. Additionally, the smooth surface of the insulator prevents water from collecting.

What’s this doing here? It looks like an ordinary automotive sparkplug. These bolt-like things were made by Western Electric and called “sparkplugs” by telephone employees. But they are not really sparkplugs. They are “bridging connectors” once used to tie the drop wire to the old-fashioned open-lead telephone wires running between the poles. The drop lead is the pair of telephone wires that goes from the telephone pole to your home or business.

Fourth Display Case

The memorabilia continues in this display case.

Field phones, toy trucks and an AT&T Annual Report in Braille are among the items in this case.

Braille report Each year AT&T issued an annual report This 1979 copy, written in Braille, was issued sight impaired individuals.

Radioactive? Our National Security relies on the ability to communicate. Maintaining our telephone communications plays a large roll. The Civil Defense program required the ability to maintain our systems under all conditions. Radiation detectors were used for testing, when necessary, to allow safe accesses for our personnel.

Military communication Military field communications employed portable telephone sets. This World War I field phone was manufactured in Germany by Siemans-Halske.

Models or toys? These telephone trucks are modeled after vehicles in the Company fleet of days gone by.

Old Paper Of days gone by, two reams of “Bell System” watermarked stationary still in their original wrapper.

Click here to move to the next page of this exhibit, or use the following links to jump to rooms in this exhibit. Hover over the links for short descriptions of each page.

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PICTURED: (above, beginning of article) The third display case on the second floor of The Museum of Communications, Seattle.
PICTURED: (throughout article) The images on this page are described fully in the text. Click the images to enlarge them.