Strowger Patents Automatic Dial Telephone System

Date March 11, 1891

Almon Brown Strowger’s automatic dialing system provided one-wire signaling that ultimately proved to be a practical way to provide automatic switching on the Bell telephone network.

Locale Kansas City, Missouri

Key Figures

• Almon Brown Strowger (1839-1902), Missouri undertaker who invented automatic telephone dialing
• A. E. Keith (fl. late nineteenth century), Strowger’s associate who helped refine Strowger’s invention
• John Erickson (fl. late nineteenth century) and
• Charles J. Erickson (fl. late nineteenth century), engineers who developed Strowger’s invention commercially

Summary of Event

After Alexander Graham Bell invented the telephone, much of the research and development in the growing telephony industry was directed to the need for switching equipment that would provide reliable and convenient access for increasing numbers of users linked to growing telephone networks. During the decade and a half that followed Bell’s first dramatic demonstration of the telephone in 1876, all telephone calls between two points had to be manually connected by operators—a bottleneck that often resulted in delays and other problems during times of peak telephone use.

Telephone subscribers also realized that, during periods of high demand, operators were in a position to control which users would get priority access. Users were also concerned about privacy and fairness. Operators could listen in on conversations and were in a position to control whether calls even went through. Some subscribers expressed concern that operators might be tempted to become involved in schemes concocted by third parties to interfere with, or even sabotage, competition among commercial establishments. That concern was expressed by Almon Brown Strowger, a Kansas City, Missouri, undertaker who, despite a lack of technical training and expertise, set out to invent a way for telephone users to bypass operators automatically to ensure that calls would go through and that they would be private.

Strowger had become convinced that his own funeral business was being victimized by unscrupulous telephone operators who were deliberately giving incorrect phone numbers to callers attempting to reach him, or, when correct numbers were requested, engaging busy signals rather than putting the calls through. Recognizing that the only recourse was to find a way to bypass human operators, Strowger determined to invent an automatic switching system capable of doing just that.

All previous attempts to develop automatic switching systems had failed. In 1879, for example, the Connolly-McTighe patent, issued on December 9 to M. D. Connolly, T. A. Connolly, and T. McTighe, had provided specifications for the first automatic telephone switch, but it ultimately proved a failure. In 1884, Ezra Gilliland developed a primitive system that proved reliable but inefficient. It worked but was capable of serving only fifteen telephones. Strowger learned from those ideas when he proposed and patented a system that could handle up to ninety-nine telephones on March 11, 1891.

Each Strowger telephone had two buttons that could be pressed up to nine times each to achieve the required digits for any two-digit number from zero to ninety-nine. In the telephone central office, each electric pulse created when the buttons were pushed moved a mechanical arm so that the contact points were placed directly in line with those of the exact numbers requested. This innovation was quickly accepted as the key to automatic switching, and in 1891 Strowger set up the Strowger Automatic Telephone Exchange to exploit his patent by manufacturing the switches designed according to the specifications set forth in his patent. That company would be absorbed into the Automatic Electric Company in 1908.

Strowger’s automatic switch was not a complete success initially, although the underlying principle upon which it was based was sound. Shortly after acquiring the patent, Strowger became associated with A. E. Keith, John Erickson , and Charles J. Erickson. All were talented engineers who helped develop his automatic switch concept into a workable and dependable system. In November, 1892, the first Strowger system was installed in LaPorte, Indiana, making it the first automatic central switching facility in the world. Over the next fifteen years, the system was repeatedly tested, modified, and remodified.

Around the turn of the twentieth century, the American Telephone and Telegraph Company was examining and testing automatic switching systems that were being proposed by other companies. Meanwhile, the Automatic Electric Company pressed on with development and deployment of its Strowger system. It installed systems capable of handling up to six thousand lines each in several cities including Grand Rapids, Michigan, and Dayton, Ohio.

Despite the growing track record of the Strowger system, the future of automatic switching was seen as uncertain by the Bell company, which had set up its own automatic systems in many small towns and rural areas. These systems had proved less reliable and more costly than manual switching because they required constant technical maintenance and support, and they did not eliminate completely the need for manual operators. To early telephone designers, this meant that automatic switching was not a true substitute for manual switching. Instead, it was perceived to be simply a costly enhancement of the existing system that, over the years, had become increasingly efficient and less costly per subscriber as the numbers of telephone subscribers increased.

Bell company officials were also concerned that automatic switching put responsibility for making telephone connections on the shoulders of the customers, instead of the operators. They reasoned that that might result in the public perception that the quality of service had been lowered. From the beginning, American Telephone and Telegraph officials had insisted that automatic switching must be both cost effective and reliable and represent a tangible improvement in overall quality of telephone service for the customers.

Despite the concerns about privacy and access, manual switching centers had been evolving also. They were streamlined gradually for efficiency and cost effectiveness, often handling ten thousand lines or more. Telephone company officials remained unconvinced about the practicality of automatic switches until 1914. By that time, the Automatic Electric Company had refined and enhanced the Strowger switch to the point where it performed most of the functions of manual operators. The breakthrough came in 1905, when a new electronic pulsing scheme was incorporated that required only one wire. Until that time, two wires were required to send electronic signal pulses back and forth between stations and central switches. A timing scheme was introduced that eliminated the need for the second line, and a major advance in technical efficiency was suddenly at hand.

Strowger died several years before his automatic switching concept achieved its full potential as the primary automatic switching technology employed by the Bell system. In May, 1916, the Automatic Electric Company and Western Electric, the telephone equipment manufacturing branch of American Telephone and Telegraph, signed an agreement that gave Western Electric the right to manufacture Strowger automatic dialing equipment, although Automatic Electric would continue to supply equipment to the parent company for many years. In 1917, the Strowger switch was ordered for a new Bell central office in Norfolk, Virginia, and from that point on was the accepted switching technology in all Bell system installations. Automatic Electric continued to supply equipment to Bell until 1936.

Significance

The Strowger automatic dialing system represented a change from the way telephone service had been provided during the early years. Bell officials had assumed that manual operators would always be involved in connecting calls because the system was too technically complicated for most subscribers to master. During those years, subscribers simply picked up their telephone receivers and gave quick pulls on hand cranks to signal operators to come on the line. Callers then gave the operators the numbers—or sometimes only the names—of the parties they wished to reach, and the operators placed their calls.

Station dialing required callers to do everything. They had to punch in the numbers of the desired parties accurately and then wait for the connections to go through. This process was complicated when long-distance toll calls were placed, and company officials worried that the public would perceive automatic dialing to be a degradation in the quality of the service to which they had become accustomed.

By 1914, Bell operators were discovering that a significant portion of the public had already been exposed to automatic dialing with few complaints about the added effort of station dialing. For almost fifteen years, the Automatic Electric Company had been selling ever-improving Strowger equipment to independent telephone companies around the country that could not afford to employ full-time operators. That equipment had gained a good reputation among the independent companies for reliability and economy, and was particularly valuable in systems where peak demand could not be handled efficiently by manual operators. During the same period, Bell was buying up many of these independents, in the process acquiring the installed equipment. Telephone subscribership was continuing to skyrocket, and, in desperate need of a way to accommodate that growth, the company began to run its own tests and use the Bell Research Laboratory to refine the Strowger concept for use on the nationwide system. That the concept ultimately became the basis for the design of the automatic rotary dial telephone bears witness to the significance of the unique and innovative ideas proposed by Strowger.

Bibliography

Brooks, John. Telephone: The First Hundred Years. New York: Harper & Row, 1976. Excellent corporate history of the Bell telephone system that includes many anecdotes and colorful stories about the early years of telephony, giving life and context to otherwise highly technical descriptions.

Casson, Herbert. The History of the Telephone. Chicago: A. C. McClurg, 1910. Rare glimpse into the early days of telephony as described by many of the innovators who participated in the development of the nationwide telephone network.

Danielian, Noorbar R. AT&T: The Story of Industrial Conquest. New York: Vanguard Press, 1939. Good look at some of the personalities involved in the development of the world’s largest telephone network.

Fagen, M. D., ed. A History of Engineering and Science in the Bell System: The Early Years, 1875-1925. New York: Bell Telephone Laboratories, 1975. Large work prepared by the Bell technical staff as part of a multivolume set tracing the corporate and technical history of the company. Contains detailed and well-illustrated descriptions of the Strowger dialing apparatus from the very first prototype through its evolution to the rotary dialing mechanisms still in use.

Hill, R. B. “Early Work on Dial Telephone Systems.” Bell Laboratories Record 31 (March, 1953). A good overview of the technical developments in dial switching during the earliest years.

‗‗‗‗‗‗‗. “The Early Years of the Strowger System.” Bell Laboratories Record 31 (March, 1953). Good overview of the technical developments in dial switching during the earliest years.

Rhodes, Frederick Leland. Beginnings of Telephony. New York: Harper & Bros., 1929. Another early look at behind-the-scenes research and development that shaped telephone technology during its first quarter century.