19th century illustration of French scientist and physiologist Etienne-Jules Marey's (1830-1904) sphygmograph. A sphygmograph is a mechanical device that was used to measure blood pressure in the mid-19th century. Marey improved on the first sphygmograph, developed in 1854 by German physiologist Karl von Vierordt (1818-1884), by making the device portable. He also included a specialized instrument to be placed above the radial artery that was able to magnify pulse waves and record them on paper with an attached pen. Illustration published in Nouveau Dictionnaire De Medecine Et De Chirurgie Pratiques by Sigismond Jaccoud, Volume 33, 1882.