Due to his traumatizing observations of surgery as a student, he decided to experiment with anesthetics. He tried using ether and chloroform, but refused to use ether due to its bad odor. He discovered the anesthetic properties of chloroform, using it in obstetrics, to make childbirth easier and safer. He also invented a new design for the forceps, to make them safer to use. They are now known as "Simpsons' forceps". He was one of the earliest doctors to use midwifes in hospitals. 