During World War I, Smyth worked in the Chemical Warfare Service, and at the
Aberdeen Proving Ground. After earning his second PhD, he returned to Princeton for the last year of his NRC fellowship. Smyth's early research was in
spectroscopy, focusing on
ionization of gases by impact with
electrons as a means to study the gases' critical
energy levels. He published his first research article, on the radiating potentials of
nitrogen gas, in 1919; this became the basis of his first
dissertation. In a 1922 article, he described a method for determining the
ionization energy of a molecule using
anode rays and demonstrated the method on
mercury vapor. In the following year he used this same method to study nitrogen. He also published on the ionization of
hydrogen,
carbon dioxide,
nitrous oxide,
nitrogen dioxide,
water vapor,
sulfur dioxide, and
carbon disulfide. As
Robert H. Dicke,
Val Logsdon Fitch, and
Rubby Sherr wrote in 1989, "By 1935 his 30 published papers established him as a leading
experimentalist" in the field. In 1929
Kenneth Bainbridge completed his PhD dissertation at Princeton working under Smyth, using anode rays to search for
element 87. In the mid-1930s, Smyth began to shift his interest to
nuclear physics, inspired by
James Chadwick's discovery of the
neutron,
John Cockcroft and
Ernest Walton splitting the atom, and
Ernest Lawrence's invention of the
cyclotron. Three of his last research articles concerned detection of
triatomic hydrogen and
helium-3. His appointment as department chair forced him to devote more time to administrative work, at the expense of research.
Richard Feynman had achieved an unprecedented perfect score on the Princeton University entrance exams, and applied for admission. While department chair, Smyth questioned his admission, writing to
Philip M. Morse to ask: "Is Feynman Jewish? We have no definite rule against Jews but like to keep their proportion in our department reasonably small". Morse conceded that Feynman was indeed Jewish, but reassured Smyth that Feynman's "physiognomy and manner, however, show no trace of this characteristic". As department chair, he had two cyclotrons built at Princeton, one in 1935 and the other in 1946. He was a member of the subcommittee on physics of the National Research Council from 1928 to 1935. In 1936 Smyth responded to media criticism of
basic science research as "useless" by suggesting that seemingly useless research could turn out to be very useful later. == World War II ==