Dr. Thomas Preston (1860-1900) was an Irish scientist, notable for his 1897 discovery of the Anomalous Zeeman Effect. In addition to his work in magnetism and spectroscopy, Preston was an adept textbook author during the late-19th century when the emerging professionalization of the sciences elicited demand for formal educational materials. He published two well-known physics textbooks, The Theory of Light (1890) and The Theory of Heat (1894). Both were reprinted in several editions for widespread use across Europe and North America and remained popular long after his early death on March 7, 1900. The Theory of Light was praised for its dealings with both “propound theory and experimental facts,” similar to comparable French-languages texts from physicists Emile Verdet and Henri Poincaré. British astronomer Sir Arthur Eddington, who later earned international fame for a 1919 solar eclipse expedition which provided evidentiary support for Einstein’s theory of general relativity, called Preston’s Theory of Light, “the leading textbook of my undergraduate days.”
One contemporary reviewer described the book as “an admirable treatise” that did well to address a present “matter of considerable difficulty for American students interested in higher theoretical optics.” According to the reviewer, many past students failed in their efforts to pursue further study in the field “for want of access to the original memoirs and in the absence of any adequate presentation of their contents in any of the American textbooks.” He suggested that Preston’s Theory of Light bridged an intellectual divide between educational resources on either side of the Atlantic. A later discussion of significant science textbooks in T.H. Savory’s The Language of Science, counts Preston’s works among an “almost unparalleled series of books” published by Macmillan near the start of the 20th century. Evidence suggests The Theory of Light remained in classroom use into the mid-1950s.
The Wolbach Library’s copy of The Theory of Light contains a bookplate from Professor Robert Wheeler Willson (1853-1922), a contemporary of Preston’s and a former Harvard astronomer. Willson first entered Harvard University as a student in the fall of 1869. He graduated four years later with degrees in Physics and Chemistry. At the time, undergraduate students had almost no access to any formal astronomical education beyond a few shortened courses, but Willson was successful in his efforts to pursue further study. After spending a year assisting Benjamin Apthorp Gould at the Argentine National Observatory, Willson returned to Cambridge to work with Joseph Winlock at the H.C.O. He later relocated to Europe, where opportunities for advanced study in astronomy were more plentiful and completed his doctorate at the University of Wurzberg in 1886.
A collaborative research project with Benjamin Peirce brought Willson back to Cambridge for the third time. He began teaching courses in physics and astronomy at Harvard in 1891, a year after Pierce’s Theory of Light went to publication, and his were among the first substantial undergraduate courses ever offered in astronomy at Harvard. By 1899, Willson received a formal appointment to Assistant Professor of Astronomy. He became a full Professor in the discipline four years later, and his efforts to implement practical opportunities for student-led research resulted in the establishment of the Harvard University Astronomical Laboratory. Willson served as a consultant for other institutions attempting to create similar laboratories and spent considerable time throughout the course of his career developing both tools and methodologies of instruction.
With the addition of Willson’s bookplate, the Wolbach Library’s Theory of Light brings together two scientists who offered significant contributions to student astronomical education during a key turning point in the professionalization of the field. It remains a valuable historical text and a unique artifact of that intellectual evolution.
 Eddington, Arthur Stanley. The Philosophy of Physical Science. New York, Cambridge, Eng.: Macmillan Company; The University Press, 1939.
 Savory, T.H., The Language of Science (London, 1953), p. 176. As Cited in: Weaire, D, and O’Connor, S. “Unfulfilled Renown: Thomas Preston (1860-1900) and the Anomalous Zeeman Effect.” Annals of Science 44, no. 6 (1987): 617-44.
 R.H. Whitford, Physics Texts: A Reference Manual (Washington D.C: Scarecrow Press, 1954).
 Stetson, H.T., “Robert Wheeler Willson (1853-1922).” Proceedings of the American Academy of Arts and Sciences, vol. 60, no. 14 (December 1925): pp. 658-663.