Glass insulators were first produced in the 1840's to support
telegraph lines. Later as time went on they were used for telephone
lines, power lines which included street lighting, street railways,
trolleys, and interurban lines. Also for fire and police alarm
circuits and even electric fencing. Along railroads glass insulators
were used for telegraph, telephone, signaling (controlling), and power
use. Basically any electric line that was needed to support insulators
for electrical leakage.
This is one of my display cabinets showing the different colors of glass insulators.
You really have to see this in the large photo size.