Palmer spirometer with syphon counterpoise.  Found in Palmer, C. F. 1934. Palmer Research and Students’ Apparatus for Physiology, Pharmacology, Psychology, Bacteriology, Phonetics, Botany, etc.: Manufactured by C. F. Palmer (London) Ltd., Myographic Works, 63a, Effra Road, Brixton, London, S.W. 2. England, page 54.

“This illustration shows a spirometer, embodying the Syphon Counterpoise principle devised by Tissot, arranged for use in the Bio-chemistry Department of the Middlesex Hospital.

“A light float B is connected by a cord over the pulleys C to the Counterpoise D, which slide on guide wires; a  Syphon runs from the main water tank A, through tubes E, G and F into the Counterpoise D.  It therefore follows, that as the float B, is raised the Counterpoise D falls, and water is syphoned from A into D until it is level in both, this having effect of making the Counterpoise D weigh heavier the greater the distance float B is out of the water. By carefully determining the bore and weight of the Counterpoise in relation to the float, an almost exact balance can be obtrained for the full movement of the Float.”