of fluid mechanics in an effort to make the rational mechanics approach of Truesdell, Coleman, and others more accessible to students. First Cambridge sabbatical After he had been with the department for six years, Aris took a sabbatical at the Shell Department of Chemical Engineering at the University of Cambridge during the 1964–1965 academic year, where he was able to interact with many well-known engineers and mathematicians such as Geoffrey Taylor and John Littlewood. He also lectured in many places in Europe, including Brussels, Copenhagen, and Trondheim. Second Cambridge sabbatical Aris took a second sabbatical after 6 years, again going to the University of Cambridge, during the 1971–1972 academic year. He spent his time writing a monograph on mathematical models for porous catalysts, which he did not finish until 1973. During his sabbatical, he received financial support in the form of a Guggenheim grant. This also provided Aris an opportunity to participate in the board overseeing the formation and development of Los Alamos National Lab's Center for Nonlinear Studies, which allowed Aris the opportunity to travel to Los Alamos during the 1970s and 1980s. Department chairmanship In 1974, Neal Amundson, who had been the department chairman of the University of Minnesota's Chemical Engineering department for nearly 25 years, resigned from this position. Aris was appointed acting head of the department, while Amundson left Minnesota for the University of Houston. Aris acted as department chair for 4 years, and was relieved of the position in 1978. Coinciding with this was an offer from Princeton University to join the faculty there, as well as the offer to stay at the University of Minnesota and work half-time in the chemical engineering department and half-time in the paleography department. Aris decided to stay at the University of Minnesota. Paleography In addition to his interest in chemical engineering, Aris was also interested in the humanities. At the University of Minnesota, Aris was able to pursue his interest in paleography when he was granted a professorship in the Classics Department, where he taught classes and published books and research articles. Aris published his book Explicatio Formarum Literarum, or The Unfolding of Letterforms, which covered the history of written letters from the 1st century to the 15th century. Further sabbaticals Aris had several other sabbaticals over his 40-year career. Through the Fairchild Distinguished Scholar program at the California Institute of Technology, Aris was able to spend a