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FunctionIf one instrument symbolized nineteenth century physiology, it was the kymograph. Devised by Carl Ludwig in 1846, it was a close cousin of the astronomical chronograph and other graphical recording instruments that traced time. A piece of smoked paper was attached to the drum, which revolved by clockwork. A signal from a tuning fork or physiological instrument was transmitted to a stylus that scratched a wavy line on the paper.
Kymograph means "wave writer" in Greek. The wavy tracings on the paper recorded blood pressure, heart beats, respiration, electrical conduction of nerves, and other physiological and muscular changes that varied with time. Experimental psychologists used kymographs to record response times, muscle exertions, and physiological reactions that accompanied emotions.
The tracings enabled the study of phenomena that had previously been too fleeting and faint to measure. The graphs offered scientists a non-verbal language that could be understood across different disciplines. They also had a claim to objectivity, recording events solely through instruments rather than by human observation.
According to the description found in the Harvard Physiological Apparatus catalogue, "Careful measurement with a tuning-fork shows that this kymograph is as accurate as the ordinary Beltzer [sic] kymograph. It is compact, light, and convenient. It will be ready for delivery not later than February, 1902."
Primary SourcesW. T. Porter, "An Improved Kymograph," The American Journal of Physiology 10 (1904): xxxix-xli.
W. T. Porter, An Introduction to Physiology (Cambridge: Harvard University Press, 1901), 51-54.
The Harvard Physiological Laboratory (Boston: Lord Electric Co., 1901), 32-33.