Sallie P. Mead: An Industrial Mathematician in the Early 20th Century

By Greg Coxson and William Haloupek

Sallie P. Mead (1893-1981) is sometimes recognized in the history of radar technology for providing mathematical support to George Southworth’s development of the waveguide ahead of World War II. Southworth, who was Mead’s colleague at the American Telephone and Telegraph Company’s Development and Research arm (AT&T D&R), helped to revive waveguide research in 1931 after the field had been in a relative hiatus [4]. When the U.S. joined the war effort a decade later, AT&T could support the military’s need for waveguides in radar and communications thanks to Mead’s contributions. 

So who was Sallie P. Mead? Sallie Mead was born as Sallie Eugena Pero on October 1, 1893, in Manhattan, NY, to Robert R. Pero and Lillian M. Foggin. She was their third child and first daughter; her brother Bertram became an engineer at General Electric and her brother Eugene died before she was born. According to her great-niece, Pero was a bright student who skipped grades in school. This fact helps explain how she began to study at Barnard College in 1909, one month shy of her 16th birthday.

Pero could walk to Barnard from her home, so she lived with her parents while pursuing an undergraduate degree in mathematics. She was a popular student and athlete and played a variety of sports, including field hockey, baseball, and basketball; she even won in the long jump and hurdles at the school’s annual Field Day. Upon her graduation in 1913, Pero earned the highest honors in mathematics and received Barnard’s Kohn Mathematics Prize. She then applied to Columbia University’s master’s program in mathematics rather than enter the workforce or enroll at Columbia’s Teachers College (which trained young women in industry skills). As a requirement of the one-year program, Pero prepared a master’s essay entitled “Linear Transformations and the Theory of the Tetrahedron.” This essay—which followed the work of Felix Klein [10]—developed the theory of linear transformations and the rotation group of the tetrahedron, then demonstrated how these elements enable the solution of general quartic equations.

With her master’s degree in hand, Pero gained a license to teach mathematics as a substitute in New York City schools. Her first assignment was at Evander Childs High School in the Bronx. By June 1915, however, she had a new job at AT&T’s Western Union building on Broadway. George Ashley Campbell—a Harvard-trained mathematician and one of AT&T’s most famous inventors [3]—hired Pero as a “computer” and assigned her to develop expansions of probability distributions for telephone traffic collisions. In 1923, Campbell thanked a group of young analysts for their work on the exponential Poisson distribution and gave special credit to Pero for taking the expansion out to 11 clearly meticulously derived terms [5]. It is interesting to note the other analysts that Campbell recognized at this time: Edith Clarke, the first female to earn a master’s degree in electrical engineering at the Massachusetts Institute of Technology [2]; Ron Foster, who went on to make contributions to network theory and is the namesake for Foster’s reactance theorem; and Edward Molina, a self-taught mathematician who (independent of Poisson) developed the exponential Poisson distribution. Also in 1923, Pero was elected as a member of the American Mathematical Society; the following year, she was one of only four women on the membership list who were employed in industry [16].

Job titles that were available to women in the early 1900s generally did not include “engineer.” Yet according to city directory listings and federal and state census records, Pero made the jump from “computer” to “engineer” in 1919. This was the year that World War I ended—a war in which AT&T played a significant role [9, 11, 15]—and a time of major post-war restructuring for the company. Pero was now employed in AT&T D&R’s Transmission Engineering unit under supervisor John Renshaw Carson, who remained her supervisor until his death in 1940. Pero and Carson were on seemingly equal educational footing, as Carson held a master’s in mathematics from Princeton University.

Carson sometimes receives credit for AT&T’s unusual level of management support for mathematics in engineering innovation [15]. Originally hired to help Campbell gain a patent for the electric wave filter, Carson translated the mathematics in Campbell’s application for the patent attorneys — a feat that facilitated rapid filing. 20 years earlier, Campbell had shockingly lost out on a patent for the loading coil to Serbian-American physicist Mihajlo (Michael) Pupin by two days. This failure, which cost AT&T half a million dollars in patent rights [13], was blamed on the patent attorneys’ inability to understand the mathematics behind Campbell’s invention [1].

In the 1920s, Pero developed an expertise in the mathematics of transmission through various cables, wires, and conducting tubes, especially those with circular cross sections. She also achieved a series of notable firsts. In 1924, she applied for a patent on a “distortion compensator” invention. Upon granting of the patent (US1,709,037) in 1929, Pero became the first woman at AT&T to hold a patent — the first of six patents that she would earn throughout her career. Her invention sought to undo phase deviations in long submarine cables due to the frequency differences in components of telephone communications. A 1999 posthumous paper by well-known Bell Labs engineer Sidney Darlington credits Pero’s invention as the first special-purpose equalizer [7]. In 1925, Pero also became the first woman to publish a technical report in the Bell System Technical Journal (BSTJ). By this time, she was Sallie P. Mead due to her 1924 marriage to Charles Edwin Mead, a New York City elevator inspector. Sallie P. Mead remained her professional name for the rest of her career.

With the development of television in the late 1920s, a number of engineers at AT&T D&R were involved in creating cables to support the higher frequencies and wider bandwidths of this new technology. In 1929, Lloyd Espenschied and Herman Affel received a U.S. patent for a “concentric conducting system;” they were inducted into the National Inventor Hall of Fame in 2006 for the invention of the coaxial cable. However, an additional pair of AT&T patents was filed on the same day (May 23, 1929) with similar titles, both of which were also granted. One of them was a “concentric conductor transmission system” by Carson and Mead.

In the early 1930s, the world was on the brink of a terrifying new peril. And radar, an invention that would help the Allies avert defeat in World War II, was not yet developed. The often-told story of radar is replete with serendipitous observations that scientists made while pursuing other goals. One example is the 1930s waveguide work at AT&T. To defeat German submarines and airborne threats, radar needed to employ “hyper-frequency” (now known as microwave) signals. However, the standard means of conveying signals (e.g., by cables and wires) experienced high losses at such frequencies. The solution emerged in the form of microwave waveguides.

Enter George Southworth of AT&T D&R. In 1931, he started to investigate waveguides (i.e., conducting metal tubes) with the intent to both improve communications technology and revisit phenomena from his Ph.D. work at Yale University [12]. As Southworth began to enlist help for designing and testing, his activities gained the attention of other employees at AT&T — including Mead’s supervisor. Carson initially published a technical report claiming that Southworth’s waveguides were infeasible and hence a waste of company resources; fortunately, he revisited his calculations and withdrew these claims in a follow-up report. He then assigned Mead to support Southworth’s project as an analyst. Meanwhile, Sergei Schelkunoff—a Ph.D. mathematician and Russian émigré at Bell Labs—caught wind of Southworth’s project and became interested as well.

Southworth had been unaware of Lord Rayleigh’s 1897 research [14] that could have greatly informed his project — Rayleigh had discovered that a waveguide’s dimensions determine a cutoff frequency, below which transmissions are greatly attenuated. Mead and Schelkunoff rediscovered Rayleigh’s findings not long after starting their mathematical analysis. In 1933, they observed something new and exciting: a mode in circular waveguides that behaved differently from any mode in any guided media of which they were aware. Rather than increasing with frequency as in more familiar media, attenuation actually decreased. Their excitement over this discovery is evident in a BSTJ technical report that they published with Carson in 1936, entitled “Hyper-Frequency Wave Guides – Mathematical Theory” [6]. Southworth’s project gained company support, and by the beginning of World War II the government was contracting with AT&T for waveguides to support radar and other military needs.

In January 1934, Charles Mead passed away from pneumonia. Four years later, Mead married architectural draftsman and surveyor Chester E. Grant. She continued to use the name Sallie P. Mead for most professional cases.

During World War II, Mead was assigned to the development of fire control systems, which automatically tracked incoming rockets and other threats. In early 1942, The Newark Evening News interviewed several professional women at AT&T, including Mead. The resulting article was titled “Women Research Experts Shoulder Invisible Guns for Our Defense.”

After the end of World War II, Mead was reassigned to the Traffic Department to conduct probabilistic studies of communication traffic; in some sense, this move returned her to where she had started at AT&T. In 1958, she retired at the requisite age of 65. She had joined the company as a human computer in 1915, at a time when young female computers usually lasted only a few years. Defying all odds, Mead retired after a successful 43-year career. In her retirement announcement in the Bell Laboratories Record, she remarked that she looked forward to having more time to study Russian and mathematics [17].

Mead passed away in New Jersey in April 1981, after a long and active retirement and an even more active career.

---

References
[1] Brittain, J.E. (1970). The introduction of the loading coil: George A. Campbell and Michael I. Pupin. Technol. Culture, 11(1), 36-57.
[2] Brittain, J.E. (1985). From computor to electrical engineer: The remarkable career of Edith Clarke. IEEE Trans. Edu., 28(4), 184-189.
[3] Brittain, J.E. (2007). Electrical Engineering Hall of Fame: George Ashley Campbell [Scanning our Past]. Proc. IEEE, 95(5), 1133-1137.
[4] Brittain, J.E. (2010). Electrical Engineering Hall of Fame: George C. Southworth [Scanning our Past]. Proc. IEEE, 98(10), 1787-1790.
[5] Campbell, G.A. (1937). The collected papers of George A. Campbell. New York City, NY: American Telephone and Telegraph Company.
[6] Carson, J.R., Mead, S.P., & Schelkunoff, S.A. (1936). Hyper-frequency wave guides – Mathematical theory. Bell Syst. Tech. J., 15(2), 310-333.
[7] Darlington, S. (1999). A history of network synthesis and filter theory for circuits composed of resistors, inductors, and capacitors. IEEE Trans. Circuits Syst., 46, 4-13.
[8] Fortiner, V.J. (1942, March 13). Women research experts shoulder invisible guns for our defense. Newark Evening News, p. 28.
[9] Gertner, J. (2012). The idea factory: Bell Labs and the great age of American innovation. London, U.K.: Penguin Press.
[10] Klein, F. (1993). Vorlesungen über das ikosaeder, und die auflösung der gleichungen vom fünften grade. Basel, Switzerland: Birkhäuser.
[11] Millman, S. (Ed.) (1984). A history of engineering and science in the bell system: Communications sciences (1925-1980). Indianapolis, IN: A.T.&T. Bell Laboratories.
[12] Packard, K.S. (1984). Origins of waveguides: A case of multiple rediscovery. IEEE Trans. Microw. Theory Tech., 32(9), 961-969.
[13] Pupin, M.I. (1922). From immigrant to inventor: Autobiography of the Serbian-American physicist, chemist and pioneer of electrical transmission and the long-distance telephone line. Pantianos Classics.
[14] Rayleigh, Lord (1897). On the passage of electric waves through tubes. London, Edinburgh, Dubinc Phil. Mag. J. Sci., 43, 125-132.
[15] Reich, L.S. (1985). The making of American industrial research: Science and business at GE and Bell, 1876-1926. Cambridge, U.K.: Cambridge University Press.
[16] Richardson, R.G.D. (1924). The thirtieth annual meeting of the Society. Bull. Am. Math. Soc., 30, 199-216.
[17] Schindler Jr., G.E. (Ed.). (1958). Sallie P. Mead [retirement announcement]. Bell Laboratories Record, 36(11), p. 23.

Greg Coxson is a professor in the Electrical and Computer Engineering Department at the U.S. Naval Academy. He previously worked as a radar analyst at Hughes Radar Systems, Lockheed Martin, the Radar Division at the U.S. Naval Research Laboratory, and Technology Service Corporation. He holds a Ph.D. in electrical engineering and a master’s in mathematics from the University of Wisconsin, as well as bachelor’s degrees in physics and mathematics from the University of Virginia.

William Haloupek, now retired, has previously worked as an assistant professor at the University of Wisconsin-Stout and the College of New Jersey, as well as a senior engineer at Lockheed Martin and Raytheon. His research addressed radar discrimination, radar waveforms, orbital mechanics, rotational mechanics, and pulse compression codes. Haloupek earned a Ph.D. in mathematics from the University of Wisconsin-Madison, a master’s in mathematics from Texas Tech University, and a bachelor’s degree in mathematics from Missouri State University.