The glass insulator was an important part of the telegraph system. Electrical signals were sent through metal lines. There was danger of the line shorting out with wire placed next to wood, especially if the wood was wet. The glass provided a non-conductive layer between the wire and the wood of the telegraph pole. This prevented shorting out of the line since glass is a poor conductor and dries fast. The wire was wrapped around the glass in the wire groove. The above picture shows the insulator screwed into a wooden post inside Winsor Castle. The other picture shows one of the old telegraph poles with its glass insulator and the line connected to Winsor Castle.
The pioneers used the glass insulators for their telegraph system. In some areas, they tried to create superstition about the telegraph wires among the local Indians so they would not damage any part of the system.