© Mark Ollig
Bell-shaped glass insulators played an essential role during the early years of the telephone network.
Glass insulators were used when attaching bare iron wires to telephone poles. They prevented short circuits and corrosion by insulating the wires from each other and the pole.
Additionally, glass insulators prevented electrical current loss during the transmission of telephone calls.
The “pony” insulator, also known as style-9, made of annealed tempered glass, was commonly used by telephone companies.
The 3/16-inch thick glass insulator weighs about nine ounces and measures 3.38 inches high and 2.25 inches wide. It has a rounded single groove encircling its circumference and a petticoat-shaped flare skirt bottom.
A 1.7-inch bulbous glass dome on the insulator is said to resemble a pony’s head.
I never understood the resemblance between a pony’s head and a glass insulator.
The insulator was screwed onto a threaded 12-inch wooden pin bracket nailed to the telephone pole.
The insulator’s glass-flared skirting protected the threaded wooden portion from rotting caused by rain and snow.
Originating from a telephone company’s switchboard or central office, galvanized iron wires were strung along the poles, connecting with homes and businesses telephones.
The wire manufacturer’s galvanization process entailed immersion of the iron wire into molten zinc, forming a long-lasting protective layer against rust and corrosion caused by harsh outdoor conditions.
On some poles, 10 iron wires were supported by 10 glass insulators placed parallel to each other along an eight-foot-long rectangular wooden cross-arm beam attached near the top of the pole.
A 12-inch insulated stranded wire was wrapped around an iron wire placed in the 1/8-inch-deep, 3/8-inch-wide groove of a glass insulator, securing it in place.
The iron wire then continued to the next insulator connection point.
The unique design of the glass insulators allowed for a sturdy, secure, and electrically insulated attachment of the wires to a telephone pole.
Various manufacturers produced the style-9 pony glass insulators.
Gray & Hemingray, a glass manufacturing firm, was founded by Robert Hemingray and Ralph Gray in 1848.
The company was renamed Hemingray Glass Company, Inc., in 1870, and it was well known for producing various glass products, including tableware, windowpanes, light fixtures, milk, soda, and beer bottles.
The company also manufactured special glass containers for storing the liquid electrolyte solution used in wet cell batteries, which provided electricity for telegraphs and telephones.
In 1892, telegraph and telephone exchanges began using the Hemingray No. 9 glass insulator manufactured in Muncie, IN.
The Hemingray No. 9 insulator was made from high-quality borosilicate glass (silica sand, boron trioxide, and soda ash) and withstood extreme temperature changes without cracking.
Its petticoat-shaped glass helps distribute weight evenly and reduces the effects of moisture and dust.
Materials used during production resulted in insulator glass appearing as clear to light aqua to aqua-blue, amber, and green.
Robert Hemingray obtained US Patent 496,652 May 2, 1893, for adding triangular glass drip points (teeth) along the base of the glass insulators, improving their performance and longevity by effectively and quickly draining rainwater off the insulator.
Drip points were added to nearly all new and existing glass insulator styles, including the Hemingray No. 9.
Hemingray Glass Company, Inc. became one of the most popular manufacturers of glass insulators in the US and worldwide.
The Hemingray No. 9 glass insulator’s reliability and quality earned it widespread popularity during the history of the telegraph and telephone industry.
The one billionth Hemingray glass insulator rolled off the production line in 1937.
By the 1950s, telephone companies were replacing galvanized iron wire with plastic-insulated copper-wired cable.
Copper wire has superior electrical conductivity than galvanized iron. It is also thinner and more flexible than a 9-gauge iron wire, making it easier to install and maintain.
I recall working with mostly 22 and 24-gauge copper telephone wiring.
Copper-wired telephone cables attached to poles transmit voice signals over long distances and, unlike iron wire, do not require glass insulators.
By 1955, the last Hemingray No. 9 glass insulator was produced, and in 1966, the company’s manufacturing plant closed.
Porcelain is the most widely used material for electrical insulators by power utilities today.
Hemingray No. 9 glass insulators are now considered valuable collectibles and remembered for their importance in constructing the telegraph and telephone network.
When I worked at the Winsted Telephone Company, I installed and removed many green glass insulators with the markings “Hemingray No. 9” on one side and “Patent May 2, 1893” on the other.
While going through my old Graybar Telephone Catalog from 1957, I stumbled upon a description of the Hemingray No. 9 glass insulator on page 137. It was labeled as “Pony. Single-groove, single petticoat. Lightweight for rural telephone lines.”
I picked up and stared closely at one of the glass insulators in my collection, and for a moment, it resembled a pony’s head.
