Argument The sphygmograph as designed and tested by Jules-Étienne Marey - an apparatus destined to write pulse tracings on paper - revolutionized medical diagnostics in the early 1860s. Since the accuracy with which this device registered and objectified the pulse was controversial from the outset, the young scholar Ernst Mach (soon to become a leading theoretician and philosopher) decided to thoroughly examine Marey's sphygmograph. The investigation led to the invention of an alternative, truly Machian, sphygmograph. Mach's sphygmograph had originated in the regime of theoretical and applied physics, whereas the instrument invented by Marey had been rooted in the regime of experimental physiology. This one type of instrument thus serves as the focal object of a comparative study of two antagonistic epistemological approaches to sphygmography.