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To contain electricity, you need insulators. Before electricity was made, there was the Big Electricity to deal with: lightning! So, the earliest glass insulators were LRIs (Lightning Rod Insulators), used to insulate lightning rods and cables from structures. They date to the 1840s or earlier, and were made in glass until about the turn of the century. Group of Lightning Rod Insulators (LRIs)
Lightning Rod Insulators
Group of battery rest insulators
Battery Rest Insulators
In 1844, Morse's first telegraph line was installed between Baltimore and Washington. To produce the current needed, wet cell DC batteries were used: glass tanks full of electrolytic solution with copper, carbon, or zinc electrodes. These batteries were often insulated from their supports with "battery rest insulators". See Richard Dawson's display for more.
The early years of telegraph development saw rapid change in insulator design: it wasn't yet known what worked well, or why. Many designs were fine when first installed (usually during mild, dry weather), but failed quickly in the wet season, or became damaged due to big temperature swings. "Ramshorn" patterns (which held the wire suspended beneath) were the most popular, and were made through the 1870s. Group of three early glass insulators: Lefferts ramshorn, Wade with wooden cover, glass block
3 Early Telegraph Insulators
Group of threadless insulators
Threadless Insulators
Eventually one general design proved superior: an inverted cup shape with a groove where the line wire is attached with a tie wire, and placed on a wood "pin": a "pin-type" insulator. The insulator was glued to the pin with molten sulphur, tar, burlap, etc, and the pin set in a hole in a crossarm. Since the pin-hole was plain and smooth, these are called "threadless".
The problem was the glueing: it's very difficult to get something to stick to smooth glass. The insulators would work loose, and in cold weather when the line wire shrank, would pop off the pins. In 1865 Louis Cauvet patented the idea of threading both the pin-hole and pin, thus securing the insulator. This was the last major design change: insulators stayed about the same until their production ended in the 1970s. Group of threaded insulators
Threaded Insulators