in glasgow he gave extramural lectures for the university, on physiology, botany, materia medica, and chemistry. his great abilities, enthusiasm, and use of practical demonstrations for instruction, made him a successful and highly popular teacher, attracting large classes. at the same time he also maintained a medical practice. in 1747, cullen was awarded britain's first independent lectureship in chemistry and was elected president of the faculty of physicians and surgeons of glasgow. in 1748 while in glasgow, cullen invented the basis for modern refrigeration, although is not credited with a usable application. in 1751 he was appointed professor of the practice of medicine, although he continued to lecture on chemistry.