Almon Strowger

from Wikipedia, the free encyclopedia
Almon Strowger

Almon Brown Strowger (born October 19, 1839 in Penfield , New York ; † May 26, 1902 in Saint Petersburg , Florida ) developed the electromechanical rotary dial in 1889 , which is the technical basis for the world's first automatically operating telephone exchanges .


Little is known about his early life. From the traditional white tombstone with the inscription 'Lieut. AB Strowger, Co. A, 8NY Cav. ' it appears that he was a veteran of the U.S. Civil War . He is believed to have participated in the Second Battle of Bull Run near Manassas, Virginia .

After the civil war, he appears to have been a country school teacher before he became an undertaker. According to various sources it has in El Dorado ( Kansas ), Topeka and finally in Kansas City , Missouri , lived. It is not known where he got the idea for an auto attendant, but patent records identify him as a resident of Kansas City on March 10, 1891.

Strowger is consistently referred to as the Kansas City funeral director who invented the automatic telephone attendant system.

It is said that he was motivated to develop an automatic telephone operator because he had difficulties with the staff of the manual operator at the time. He was convinced that the operator of the local operator preferred to direct calls to his competitor. He also suspected that the intermediaries were influencing the telephone customers' selection of the undertaker when such services were required. This suspicion originated in an incident in Topeka when a friend died and the family contacted a competitor. According to other traditions, the wife or possibly the cousin of a competitor worked as a telephone operator. The exact course of events can no longer be reconstructed. Historians report that those who knew Strowger described him as eccentric , choleric, and even crazy.

With the intention that the subscribers should decide for themselves who to call instead of the operator, he began working on his invention in 1888 and was granted US Patent No. 447,918 on March 10, 1891 for an Automatic Telephone Switching System. It is reported that his first model consisted of a round collar box and some knitting needles.

While developing the idea, Strowger did not work alone; instead, he enlisted the help of his nephew William and others who knew about electricity and had the money to implement his concepts. With their help, the Strowger Automatic Telephone Exchange Company was founded, which installed the world's first commercially used automatic exchange in La Porte, Indiana , and put it into operation on November 3, 1892 with around 75 participants and a capacity for 99 participants.

The engineers developed Strowger's designs further and filed several patents under the employee's name. The company changed its name several times. Strowger himself does not seem to have been involved in the further development. He sold his patents in 1896 for $ 1,800, in 1898 his stake in the Automatic Electric Company for $ 10,000, and for health reasons he moved to St. Petersburg, Florida, where he worked again as an undertaker, according to records from HP Bussey Morgue from 1899. Strowger died of an aneurysm in St. Petersburg, Florida, aged 62 after suffering from anemia . He left some wealth behind, it is said that he owned at least one block in town.

He was survived by his widow Susan A. Strowger (* 1846 , † April 14, 1921 in Tampa , Florida ). In 1916, his patents traded for $ 2.5 million. The obituary for his wife in the St. Petersburg Times alleged that she withheld further revolutionary developments from her husband because only others would benefit from his developments. She said her husband only received $ 10,000 for his invention when he should have received a million.

A bronze plaque commemorating his invention was affixed to his grave by telephone company representatives in 1945 . Strowger was inducted into the US Independent Telephone Association Hall of Fame in 1965. In addition to the voter he invented, his name also bears a locomotive and a company award.

The Strowger patent

Sketch from his patent for the lever dial
Replica of the rotary dial exhibited in the Deutsches Museum in Munich

His patent consists of the following components:

  1. A subscriber device with one key each for hundreds, tens and units of the desired number.
  2. Each of the four buttons is connected to the exchange with its own line. A line for voice transmission is also required.
  3. A rotary dial is installed in the exchange for each participant . The selector consists of a movable contact arm and a matrix of contacts arranged on the inside of a cylinder. Each subscriber connected to the exchange has an associated contact in the matrix. The arm is connected to the caller's speech circle and can connect to any subscriber with a linear stroke and semicircular rotation.

For example, to dial the number 432, the caller presses the 100 key four times, the 10 key three times and the 1 key twice. Using a mechanism consisting of electromagnets, racks and gears, the contact arm first moves four rows upwards according to this example, then performs a rotary movement over 30 positions and then over two positions.

The system was later supplemented by line finders, which drastically reduced the number of voters required; a mechanism for recognizing a busy voter or participant has been added for this purpose. The basic concept, however, remained the same until the introduction of electronic switching technology and was in use for around 100 years. The modularization and scalability made the Strowger system far superior to the competition, whose systems were not suitable for setting up large networks.


Strowger is said to have said the following in 1890 (freely translated): "My competitor will no longer be able to steal all my customers just because his wife is a Bell operator".

Web links