US Patent 26754 by Augustus Eckert of Dayton, Ohio. 1860. A non counter-weighted water-seal spirometer. Two of the patentable features were a guide rod (B) to keep the inner bell straight and an air-filled water-tight chamber in the rim of the bottom of the inner bell (buoy, E) that served the same purpose as a counter-weight. The cork (D) was removed after a vital capacity effort had been made and recorded to allow the bell to be returned to its lower position.