The medical thermometer began as an instrument more appropriately called a water thermoscope, constructed by Galileo Galilei circa 1592–1593.

His models were bulky, impractical and took a fair amount of time to take an accurate oral reading of the patient's temperature.

[2][5] Working independently of Celsius, the Lyonnais physicist Jean-Pierre Christin, permanent secretary of the Académie des sciences, belles-lettres et arts de LyonFR, developed a similar scale in which 0 represented the freezing point of water and 100 represented boiling.

[8][9][10] The medical thermometer was used by Dutch chemist and physician Hermann Boerhaave (1668–1738), as well as his notable students Gerard van Swieten (1700–72) and Anton de Haen (1704–76).

However, his proposals were not met with enthusiasm by his peers and the medical thermometer remained a scarcely used instrument in medicine.

Between 1866 and 1867, Sir Thomas Clifford Allbutt (1836–1925) designed a medical thermometer that was much more portable, measuring only six inches long and taking only five minutes to record a patient's temperature.

[1][2] In 1868, German physician, pioneer psychiatrist, and medical professor Carl Reinhold August Wunderlich published his studies that consisted of over one million readings from twenty-five thousand patients' temperatures, taken in the underarm.

The normal temperature varies slightly with the location; an oral reading of 37 °C does not correspond to rectal, temporal, etc.

[13] Oral temperature may only be taken from a patient who is capable of holding the thermometer securely under the tongue, which generally excludes small children or people who are unconscious or overcome by coughing, weakness, or vomiting.

If the patient has drunk a hot or cold liquid beforehand time must be allowed for the mouth temperature to return to its normal value.

Previously, if doctors wanted to record an accurate brain temperature, electrodes needed to be attached to the patient's hypothalamus.

[19] Temporal artery thermometers, which use the infrared principle report temperature, are becoming increasingly common in clinical practice because of their ease of use and minimal invasiveness.

Because of the variability of technique and environmental considerations, measurements by temporal artery thermometers may suffer issues of precision, and to a lesser degree accuracy.

Temporal thermometers have been found to have a low sensitivity of around 60–70%, but a very high specificity of 97–100% for detecting fever and hypothermia.

[21] The traditional thermometer is a glass tube with a bulb at one end containing a liquid which expands in a uniform manner with temperature.

When the temperature falls, the column of liquid breaks at the constriction and cannot return to the bulb, thus remaining stationary in the tube.

After reading the value, the thermometer must be reset by repeatedly swinging it sharply to shake the liquid back through the constriction.

Phase-change thermometers use samples of inert chemicals which melt at progressively higher temperatures from 35.5 °C to 40.5 °C in steps of 0.1 °C.

They are mounted as small dots in a matrix on a thin plastic spatula with a protective transparent cover.

A typical inexpensive electronic ear thermometer for home use has a displayed resolution of 0.1 °C, but a stated accuracy within ±0.2 °C (±0.35 °F) when new.

Platinum is the most commonly used material because it is nearly linear over a wide range of temperatures, is very accurate, and has a fast response time.

Disadvantages include a smaller overall temperature range, higher initial cost, and a less rugged design Thermocouples

The metal pair generates a net thermoelectric voltage between their opening and according to the size of the temperature difference between the ends.

•Advantages of thermocouples include their high accuracy and reliable operation over an extremely wide range of temperatures.

•Disadvantages include errors caused by their use over an extended period of time, and that two temperatures are required to make measurements.

Other electronic thermometers work by remote sensing: an infrared sensor responds to the radiation spectrum emitted from the location.

This allows small changes in body temperature to be detected Glass oral thermometers typically have markings every 0.1 °C or 0.2 °F.