When a thermometer was used to measure the temperature of a liquid or of air, the thermometer was kept in the liquid or air while a temperature reading was being taken. Obviously, when you take the temperature of the human body you can't do the same thing. The mercury thermometer was adapted so it could be taken out of the body to read the temperature. The clinical or medical thermometer was modified with a sharp bend in its tube that was narrower than the rest of the tube. This narrow bend kept the temperature reading in place after you removed the thermometer from the patient by creating a break in the mercury column. That is why you shake a mercury medical thermometer before and after you use it, to reconnect the mercury and get the thermometer to return to room temperature.
In 1612, the Italian inventor Santorio Santorio
invented a mouth thermometer and perhaps the first crude clinical thermometer. However, it was both bulky, inaccurate, and took too long to get a reading.
The first doctors to routinely take the temperature of their patients were: Hermann Boerhaave (1668–1738), Gerard L.B. Van Swieten (1700–72) founder of the Viennese School of Medicine, and Anton De Haen (1704–76). These doctors found temperature correlated to the progress of an illness, however, few of their contemporaries agreed, and the thermometer was not widely used.
First Practical Medical Thermometer
English physician, Sir Thomas Allbutt (1836–1925) invented the first practical medical thermometer used for taking the temperature of a person in 1867. It was portable, 6 inches in length and able to record a patient's temperature in 5 min.
Pioneering biodynamicist and flight surgeon with the Luftwaffe during World War II, Theodore Hannes Benzinger invented the ear thermometer. David Phillips invented the infra-red ear thermometer in 1984. Dr. Jacob Fraden, CEO of Advanced Monitors Corporation, invented the world's best-selling ear thermometer, the Thermoscan® Human Ear Thermometer.