During the 1950s Baker and W.Prager of Brown University published a two volume account of the history of steel structures, with plastic theory integral to it. By the 1960s it was being taught in the undergraduate engineering course at Cambridge University, and Baker presented an undergraduate lecture on the principles of design of the Morrison shelter as an interesting introduction to his theory of plastic design of structures; in 1968 this lecture was attended by Prince Charles, and it can be summarised as follows: