By the time that he became head of the Museum as its first Principal Librarian, in 1756, Knight had acquired a considerable reputation as a scientist and inventor, developing new processes related to magnetics. He was a Fellow of the Royal Society, an institution then much involved in the Museum. Visitors touring the Museum from 1759 would be taken through a ground floor room with ‘some Sea Compasses, improved by Dr Knight, such as are now used in the Royal Navy; and several Magnets and Apparatuses, serving to shew the magnetical Powers in philosophical Uses’, (‘Guide’, 1761). These compasses, although sometimes regarded unfavourably by seamen, remained official issue for the Royal Navy until the nineteenth century.

This portrait was executed by the celebrated painter Benjamin Wilson, a school friend from Leeds who shared Knight’s interest in science, being particularly concerned with the exploration of static electricity.