Thévenot invented the spirit level (or bubble level) some time before 2 February 1661, which he filled with alcohol and mounted on a stone ruler fitted with a viewing lens. This date can be established from Thévenot's correspondence with scientist Christiaan Huygens. Within a year of this date, the inventor circulated details of his invention to others, including Robert Hooke in London and Vincenzo Viviani in Florence. It is occasionally argued that these bubble levels did not come into widespread use until the beginning of the 18th centurythe earliest surviving examples being from that timebut Adrien Auzout had recommended that the Académie Royale des Sciences take "levels of the Thévenot type" on its expedition to Madagascar in 1666. It is very likely that these levels were in use in France and elsewhere long before the beginning of the 18th century.