A set of Perkins Tractors in their original case dating to the end of the 18th century. Each is marked “PERKINS PATENT TRACTORS” less clear on the steel than the brass rod.

Elisha Perkins gave us one of history’s most salient examples of the influence of quackery. He claimed the rods were made of rare metal alloys and he peddled them as a panacea which would “draw off the noxious electrical fluid that lay at the root of suffering”. They were not, and did not. But despite their lack of effectiveness he obtained a medical patent for them, published literature and with the help of his son, successfully marketed them throughout America and Europe. The story is legend, and the tractors which were once in plentiful supply are now few and far between.

• From the Phisick collection