Concrete-shell structures consist of a thin membrane of concrete in compression. The earliest practical applications of concrete shells in architecture took place in Germany during the early 1920s. The basic mathematical formulas for shell designs were developed by Franz Dischinger and Ulrich Finsterwalder, employees of the Dyckerhoff- Widmann engineering firm. Dischinger, along with Walther Bauersfeld of the Carl Zeiss Encyclopedia of 20th-century architecture 560 Optical Company, designed the first major concrete-shell roof for the Jena Planetarium in 1924. To create the 82-foot hemispherical dome, a thin layer of concrete was sprayed over a skeletal frame of reinforcement bars. This technique became known as the Zeiss- Dywidag, or “Z-D,” process. By the 1930s employees at Dyckerhoff-Widmann, along with engineers in Spain, France, and Italy, began designing other forms of concrete-shell roofs, Kresge Auditorium Massachusetts Institute of Technology, shown from the rear, roof being re...