Professor/Inventor
G. W. Pierce had an eye for finding the main sticking point in physical processes. For electronics, he saw that resonance was a key phenomenon. His five-part series "Experiments on resonance in wireless telegraph circuits in Physical Review (1904-7) are evidence of his leadership. By 1910 his first textbook Principles of Wireless Telegraphy was published. It is in this text, and others by John Ambrose Fleming, that the term modulation is first used to describe imprinting an audio wave onto a high-frequency carrier wave by variation of amplitude of the carrier. In 1912 he worked with Arthur E. Kennelly on motional impedance (see below). In 1914, he was assigned the directorship of the Cruft Physics Laboratory at Harvard. Then in 1917 he gained the rank of professor.
The year 1920 saw two important developments: his second text Electric Oscillations and Electric Waves was published. And most significantly, he followed up on an innovation of Walter Guyton Cady of Wesleyan University, using quartz crystal to stabilise the frequency of electrical oscillation. In early attempts, radio communication was severely handicapped by the lack of reliable fixed-frequency operation, and Pierce saw the potential for the quartz-governed circuit. Cady's circuit used multiple triode vacuum tubes, and Pierce was able to reduce this to a single tube. Insights such as this one resulted in patent assignments, for which Pierce then sold license to use, yielding him the capital to purchase vacation homes in Franklin, New Hampshire, and St. Petersburg, Florida.
Motional impedance
In their laboratory, Pierce and A. E. Kennelly undertook an experiment measuring the change in impedance of telephone receivers over a range of audio frequencies when the diaphragm was clamped by finger or quill insert. At each frequency the receiver resistance and reactance were measured and impedance computed, then the difference of free versus clamped impedance plotted as a complex number, or point in the impedance plane. For every receiver, the range of frequencies yields a series of con-cyclic points. The phenomenon was called "motional impedance" and the circle a "motional impedance circle". This example of circular phenomena in device-impedance became so familiar, eventually, that the Smith Chart was introduced to provide a bounded universe (or chart) for such circles.
Later years
In 1921, he was made Rumford Professor of Physics; in 1929 he was awarded the Medal of Honor of the Institute of Radio Engineers (I.R.E.). He continued to file patents, and he reported on crystal oscillators in the Proceedings of the American Academy of Arts and Sciences in 1923 and 1925. He retired in 1940, publishing his text Song of Insects in 1943. It made an analysis of the cricket "songs". In the same year, the Franklin Institute awarded him its Franklin Medal.
For a list of publications and patents, see Saunders and Hunt (1959).