Du Fay, a Parisian by birth, started his career in the French army, rising to the rank of captain. He left to become a chemist in the Académie Française and in 1732 became superintendent of the Jardin du Roi. His great achievement was to discover the two kinds of electricity, positive and negative, which he named ‘vitreous’ and ‘resinous’. This was based on his discovery that a piece of gold leaf charged from an electrified glass rod would attract and not repel a piece of electrified amber. This was the ‘two-fluid theory’ of electricity, which was to be opposed by Benjamin Franklin's ‘one-fluid theory’ later in the century.