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Santorio Santorio and the Thermometer

Grade 7 | Informative | Text-Dependent

Source Lexile®: 1070

Learning Standards




Prompt: What was Santorio Santorio like as a person? Make a claim about what kind of person he was and defend your claim using evidence from the text.




“Santorio Santorio and the Thermometer” by Robert Mulcahy


Galileo built the first working thermoscope. He took a small glass tube filled with air and rubbed it in his hands to warm it up. Then he turned the tube over and put the open end in a small bowl of water. As the air in the tube cooled, water rose into the tube. 


Since cooler air takes up less space than warm air, there would be more space for the water as the air in the tube cooled. The water rising slowly in the tube showed that the air was cooling. When Galileo rubbed the glass tube again, the air inside would heat up, and the water level in the tube would slowly drop because the warmer air took up more space than the cooler air. Although the increase and decrease could be seen, the thermoscope could not measure the degree of the change in a mathematical way.


Despite this lack of precision, Galileo had constructed a wonderful invention. Yet, he considered it to be a useless toy and even called it a “little joke.” As far as anyone knows, the famous physicist, mathematician, and astronomer never tried to adapt the thermoscope into a device to measure the temperature of the human body.


It was Santorio Santorio, the physician who had devoted his life to measurements, who realized that he could use the thermoscope to measure body temperature. He made two important changes that transformed Galileo’s thermoscope into the thermometer.


Santorio’s first innovation was making a glass tube into which a patient could breathe. The person’s breath would heat up the air, which would push the water level down inside the tube. If the person had a fever, the water level in the tube would be pushed down farther because the patient’s breath would be hotter. Santorio colored the water in the tube green so doctors could see it more easily.


Secondly, Santorio added regularly spaced marks, or tick marks, to his device. This may appear to be a very minor addition to Galileo’s thermoscope, but it was actually a very important one. With the tick marks, Santorio could get a reading of a patient’s temperature and compare this reading to the temperatures of other patients. Or, he could compare the reading to earlier readings taken on the same patient. Santorio knew the thermometer would enable doctors to determine a person’s temperature exactly, making both diagnosis and treatment more precise. 


After inventing the thermometer, Santorio built a device to measure a person’s pulse rate. Today, people can find their pulse rates without special instruments: they only have to count how many times their pulse beats within a certain period of time. Since the clocks of Santorio’s day had no second hand, measuring time exactly was difficult.


To solve this problem, Santorio built a pendulum—a weight hanging on the end of a piece of string. Then he matched the swing of the pendulum to a person’s pulse rate by changing the length of the cord on which the weight was hanging. He improved this device by tying a knot in the cord and measuring the position of the knot on a horizontal scale. Santorio called this device the pulsilogium.


Among the many other devices Santorio built was a hydroscope, which measured the amount of water in air. To help patients who were paralyzed or had to remain immobile while healing, he invented a bag filled with water in which they could lie and bathe without moving from their bed. He also invented an instrument for removing bladder stones.


Santorio spent so much time treating patients and inventing that his students at the university accused him of not devoting enough time to his teaching. Although these charges were dismissed, Santorio was bitter over the criticism and retired from the university in 1624. As a reward for his years of outstanding work, however, the Venetian government continued to pay him his university salary for the rest of his life.


In 1630, Venetian officials asked Santorio to organize the efforts of doctors in their city to combat a plague. That same year, Santorio was elected president of the Venetian College of Physicians. On February 22, 1636, Santorio Santorio died from a urinary tract disease and was buried in the Church of the Servi in Venice. When the church was destroyed in 1812 during the Napoleonic Wars, Santorio’s skeleton was salvaged, and his skull is now in the museum at the University of Padua.

A wealthy and respected man, Santorio had never married. As he had no family, he willed his money to endow schools and fund other charities and scientific endeavors.



Excerpt from “Medical Technology: Inventing the Instruments” by Robert Mulcahy, ©1997 by The Oliver Press; pgs 21-24; ISBN 1-881508-34-X.  






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