The Purchase of the North Pole or Topsy-Turvy (French: Sans dessus dessous) is an adventure novel by Jules Verne, published in 1889. It is the third and last novel of the Baltimore Gun Club, first appearing in From the Earth to the Moon, and later in Around the Moon, featuring the same characters but set twenty years later. Like some other books of his later years, in this novel Verne tempers his love of science and engineering with a good dose of irony about their potential for harmful abuse and the fallibility of human endeavors.