"Mr. Freke would do well to enquire, before he published the next edition of his book"

John Freke (1688-1756) was elected assistant-surgeon to St. Bartholomew's Hospital in 1726, and subsequently the first curator of the hospital museum.  He was elected surgeon in 1729, and held office until 1755, when gout and infirmity compelled him to resign. Besides being one of the chief surgeons within the city of London he had a reputation as a man of learning in science, a judge of painting and of music. He made experiments in electricity and published in 1748 “An Essay to show the Cause of Electricity and why some things are Non-Electricable, in which is also considered its Influence in the Blasts on Human Bodies, in the Blights on Trees, in the Damps in Mines, and as it may affect the Sensitive Plant.

It is this book to which Fielding is referring in the quote above.