The clinical thermometer was invented by Sanctorius, an Italian physician and physiologist, who described in his 1612 book his use of the heat-measuring device. Sanctorius’s thermometer, although not the first to observe heat, was the first to measure it.
Before the last decade of the sixteenth century, there was no known way to quantify heat. All means of measuring it were subjective. About 1593, Galileo
This instrument, commonly called the air thermometer, was sensitive but inaccurate. Its inaccuracy mainly came from the unrecognized effects of barometric pressure on the unsealed system. Barometric pressure was unknown until Evangelista Torricelli
Galileo did not invent the familiar, decorative Galileo thermometer, which indicates temperature with liquid-filled glass balls rising and falling in a liquid sealed inside a glass column. This was developed later, probably by Athanasius Kircher,
In the second and third decades of the seventeenth century, Sanctorius (Santorio Santorio
The first of these four woodcut illustrations shows a Florence flask with an unusually long and thin neck inverted in an open vessel of water. The patient’s hand would enclose the bulb of the flask and within a few minutes the thermometer would react. Even though it had no scale, two threads tied around the neck could be slid up or down to record temperatures. The second woodcut is the most remarkable, as it illustrates the world’s first oral thermometer. It had a tiny bulb at the top that was placed in the patient’s mouth. The scaled neck was even longer and had four switchback curves. The length improved accuracy and the curves saved space. The third woodcut depicts a similar instrument, but with a larger bulb at the top to take the temperature of the patient’s hand. The fourth woodcut shows the least successful of the three calibrated models, with the bulb at the top replaced by a funnel into which the patient would exhale.
Physician, scientist, and scholar Santorio Santorio, best known as Sanctorius, invented medical instruments of precision, including the clinical thermometer.
Sanctorius believed that quantifying the heat of healthy as well as diseased bodies could help medical diagnoses. Keener instruments were required because correlating temperatures and other symptoms with specific ailments was the key to clinical progress in this area and because differences in body heat could be quite small. Sanctorius was one of the originators of the idea that, to be effective, medicine and its instruments must be precise. He was an iatromechanist in medicine. Iatromechanism
Sanctorius’s greatest achievement in thermometry was being the first to attempt to quantify heat by adding a scale. A Latin manuscript called Mathematica maravigliosa, written in Rome and dated 1611, contains the earliest known illustration of a calibrated air thermometer. This instrument, attributed to Sanctorius, consists of two volumetric flasks, the thinner-necked flask inverted as far as possible into the thicker-necked flask, with the column of liquid at about the midway point of the two necks. The outer neck is scaled in eight divisions of six degrees each.
Sanctorius’s experiments with calibration led to the first genuine thermometer. Strictly speaking, what Galileo invented was the thermoscope, not the thermometer, because it allowed its user to see heat but not to measure it. In 1624, Jean Leuréchon
Robert Fludd
Thermometry entered an important new phase when Jean Rey
By 1709, Gabriel Daniel Fahrenheit
Developing the means to measure changes in body temperature paved the way for rapid progress in physiology and in the clinical methods that depend upon accurate functional knowledge of physiology. Sanctorius’s contribution led directly to better understanding of the respiratory and cardiovascular systems. Iatromechanism made further progress when Giovanni Alfonso Borelli’s
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Castiglioni, Arturo. “Life and Work of Sanctorius.” Medical Life 38 (1931): 730-785. The standard biography and the most detailed treatment of Sanctorius in English. -
Chang, Hasok Chang. Inventing Temperature: Measurement and Scientific Progress. New York: Oxford University Press, 2004. A philosophical and historical analysis of the several theories of measuring temperature. -
Major, Ralph H. “Santorio Santorio.” Annals of Medical History, n.s. 10 (1938): 369-381. A eulogistic biography that highlights the development of the thermometer and other instruments. Major’s photograph collection at the Clendening History of Medicine Library, University of Kansas Medical Center, Kansas City, contains images and descriptions of several seventeenth century thermometers, including three from Santorio. -
Middleton, William Edgar Knowles. A History of the Thermometer and Its Use in Meteorology. Baltimore: Johns Hopkins University Press, 2003. A reprint of the well-reviewed 1966 edition, which, despite its title, also contains much information on the history of clinical thermometers and three chapters on the seventeenth century. -
Mitchell, S. Weir. The Early History of Instrumental Precision in Medicine. New York: Burt Franklin, 1971. A reprint of a groundbreaking medical historiography that considers the contributions of Sanctorius to the development of accurate diagnosis.
Giovanni Alfonso Borelli; Robert Boyle; Robert Fludd; Galileo; Otto von Guericke; William Harvey; Jan Baptista van Helmont; Robert Hooke; Marcello Malpighi; Santorio Santorio; Thomas Sydenham; Evangelista Torricelli.