Marey sphygmograph, 1866-1900.
© Science Museum / Science & Society Picture Library
Made by Breguet, Paris. The sphygmograph traces an undulating line, which represents a record of blood presure and pulse over time. The first practical, portable version was devised in 1860 by the French physician Etienne-Jules Marey (1830-1904) and was strapped to the wrist. This one has a lever, which rests on the radial artery in the wrist while the other end scratches the trace on to smoked paper. The paper moved at a uniform rate due to the presence of a clockwork mechanism.