New York Public Library

While still in the library school, he began working in the stacks of the New York Public Library. This began a relationship that would last for over a quarter of a century. While working at the library, he served in many capacities, including the Chief of Stacks for three years ^[9] and Assistant to the Director starting in 1919.^[10] Ultimately, in 1928 Metcalf was appointed Chief of the Reference Department. This was a position he would hold for the next ten years.^[11] While at the New York Public Library, he became interested in the use of technology in the library, when he expanded the use of the first photostat machine to the library in 1912.^[12] This innovation made the copying of documents significantly easier. He also introduced a microfilm system to the library. His goal here was primarily to save certain books from damage from heavy use. (Metcalf 1980: 279) Metcalf considered these contributions to be the things he was most proud of in his years at the New York Public Library.^[13]

Harvard University

In 1937, Metcalf was appointed Director of University Libraries at Harvard. His tenure at Harvard was where he made a significant impact to librarianship. Early on, he encountered a problem that would face many libraries – a lack of adequate space. Widener Library, the university's main library, would run out of space in a few years. In addition, the collection was so immense and the catalog so complex, it was often difficult to find materials. Metcalf recalled stories of students who were proud of the fact that they never had to use the library.^[14] Metcalf's mandate was to design a system that would meet the space needs of the library until the end of the twentieth century.^[15] The plan he came up with in 1938 was what he called “coordinated decentralization.” ^[16] While recognizing that decentralizing library services wasn't the ideal solution, he also realized that Harvard, with 76 individual collections or facilities, already was very decentralized. He became convinced that students could be well served by separate libraries, as long as each building was organized around a single topic or, in some cases, audience. To realize this plan, he proposed the construction of new facilities, including the Houghton Library for rare books in 1942, and the Lamont Library, a library designed for the needs of undergraduates in 1949. The construction of Lamont succeeded in addressing a major complaint of the university's undergraduate population – they couldn't easily find materials in Widener because of the sheer volume, or they would find that some materials were reserved for graduate students and inaccessible to undergraduates. He also expanded interlibrary cooperatives. Besides building new facilities, he also proposed splitting up Widener's collection to libraries focused on the subject matter of the material.^[17]

When planning these new facilities, Metcalf was concerned about the security of the collection – damage to manuscripts and books from variations in heat and humidity, or worst of all, damage from a flood.^[18] In the case of Houghton, the building that was to house the rare collections at Harvard, many features were designed into the air conditioning and plumbing systems that were meant to mitigate the risk of damage. Catch basins were installed under any pipe running horizontally to catch and divert any water from leaks. The plumbing system itself was designed so that the location of leaks could be found quickly through a series of shut-off valves, and the walls were designed with easy access to plumbing. The display cases themselves were designed so that they were well ventilated. This allowed lighting to be installed in the cases (rather than outside) without impacting the temperature and humidity levels.^[19] It was features like these that helped keep the collections safe.

Metcalf's experience at Harvard made him and his staff experts in the problems that were facing many research libraries at the time. ^[20] Metcalf was often called on to consult with other libraries. Harvard became the benchmark for solutions to these problems. Metcalf consulted on the libraries for the Army and Navy,^[21] and in 1942 was asked to chair a study of the University of Illinois Library School.^[22]

During this time, Metcalf was also active in the American Library Association. He served as its president in 1942 and 1943.^[23] His participation in the ALA may have contributed to Metcalf being among the first of Harvard's staff to be targeted by Senator Joseph McCarthy in his search for communists. As chair of the ALA's International Relations Board, Metcalf was asked to participate on a government committee that selected books to be included in US libraries abroad. McCarthy sought information from Metcalf on whether he had approved of the selection of a book written by Howard Fast, a Communist. If he had, would he approve it again? In his response to McCarthy, Metcalf endorsed freedom of information in all libraries, including those managed by the government, and stated plainly that if the opportunity arose, he would select Fast's book again. McCarthy never responded.^[24]

After 17 years of service, Metcalf retired in 1955 and was named Director Emeritus.^[25]

He was a member of the American Antiquarian Society from 1937 and a member of the Council.^[26]