In the mid-20th century, the focus of mathematical research and instruction moved away from the relatively simple surfaces represented by models. Engineering schools also found models of less use to their instructional purposes. Indeed, by the end of the century, computer graphics had replaced much of physical modelling. Nonetheless, as the case of models for descriptive geometry well illustrates, a rich array of mathematical treasures are now available not only through written texts but through diverse—and expanding—databases.

Acheson, Bill. 2007. “Geometric String Models of Descriptive Geometry.” In *Hands on History*, edited by Amy Shell-Gellasch, 49–62. Washington, DC: MAA.

Atzema, Eisso J., and Gerard Buskes. 2009. “‘Engel’s Ingenious Models’: on the Models of the Fresnel Wave Surface at the University of Mississippi.” *Rittenhouse* 22(1): 90–122.

Barbin, Evelyne, Marta Menghini, and Klaus Volkert, eds. 2019. *Descriptive Geometry, the Spread of a Polytechnic Art: The Legacy of Gaspard Monge*. Cham, Switzerland: Springer.

Moon, Francis C., and John F. Abel. 2016. “19th c. Olivier String Models at Cornell University: Ruled Surfaces in Gear Design.” In *Explorations in the History of Machines and Mechanisms*, edited by C. López-Cajún and M. Ceccarelli, 195–207. Cham: Springer.

Pantalony, David. 2017. “Collectors Displays and Replicas in Context: What We Can Learn from Provenance Research in Science Museums.” In *The Romance of Science: Essays in Honour of Trevor H. Levere*, edited by Jed Buchwald and Larry Stewart, 257–275. Cham: Springer.

Phipps, Barry et al. 2012. *Intersections: Henry Moore and Stringed Surfaces*. London: Royal Society of London.

Shell-Gellasch, Amy. 2003. “The Olivier Models at West Point.” *Rittenhouse* 17(2): 71–84.

Stone, William C. 1969. *The Olivier Models*. Schenectady, NY: Friends of the Union College Library.

Xavier, J. P., and E. M. Pinho. 2017. “Olivier String Models and the Teaching of Descriptive Geometry,” In *Dig Where You Stand. Proceedings of the Fourth International Conference on the History of Mathematics Education*, edited by K. Bjarnadóttir, F. Furinghetti, M. Menghini, J. Prytz, and G. Schubring, 399–414. Rome: Edizioni Nuova Cultura.

Catalogue of Olivier Models, Frederick V. Rickey, United States Military Academy (emeritus).

Conservatoire des Arts et Métiers Collections, Musée des Arts et Metiers, Paris, FR.

Ingenium Collection Online (Beta), Canadian Museums of Science and Innovation, Ottawa, ON.

Mathematical Models Collection, Department of Mathematics, University of Arizona, Tucson, AZ.

MUSEU ISEP Collections**, **Museu do Instituto Superior de Engenharia do Porto, Porto, Portugal.

National Museum of American History Collections, Smithsonian Institution, Washington, DC.

Science Museum Group Collection, Science Museum of London, London, UK.

The Collection of Historical Scientific Instruments, Harvard University, Cambridge, MA.

Historians of mathematics and museum staff who have assisted in searching specific collections are generally mentioned in the text. I thank them as well as Smithsonian colleagues, especially Judy Green and Rhoda Ratner, for their work with Smithsonian examples of the models. Finally, I am most grateful to those associated with *Convergence* for numerous improvements to the article.

After undergraduate work in physics and graduate study in the history of science, Peggy Aldrich Kidwell became a postdoctoral fellow at NMAH. She then began working in the mathematics collections, curating materials ranging from an 11th-century astrolabe to a 21st-century whiteboard. She and colleagues have written numerous articles and books on the history of mathematical instruments and computers and prepared diverse exhibits showcasing these artifacts. They also have spent much of the past decade preparing online accounts of objects.