Melchisédech or Melchisédec Thévenot was a French author, scientist, traveller, cartographer, orientalist, inventor, and diplomat. He was the inventor of the spirit level and is also famous for his popular posthumously published 1696 book The Art of Swimming, one of the first books on the subject and widely read during the 18th century. The book popularized the breaststroke ; he was inducted into the International Swimming Hall of Fame in 1990. He also influenced the founding of the Académie Royale des Sciences.

A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Two basic designs exist: tubular and bull's eye . Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some photographic or videographic work.