Instruments

Thermometer

Citation Formats

General Reference

Science Atlas. "Thermometer." Accessed August 30, 2026. https://science.interactiveatlas.org/instruments/thermometer.

APA Style

Science Atlas. (n.d.). Thermometer. Retrieved August 30, 2026, from https://science.interactiveatlas.org/instruments/thermometer

BibTeX

@misc{scienceatlas-thermometer,
  author = {Science Atlas},
  title = {Thermometer},
  year = {2026},
  url = {https://science.interactiveatlas.org/instruments/thermometer},
  note = {Accessed August 30, 2026}
}

A thermometer measures temperature. Galileo Galilei built an open thermoscope around 1592 whose liquid level rose and fell with temperature but carried no fixed scale, and it was Daniel Gabriel Fahrenheit who produced the first sealed, accurately scaled mercury thermometer in 1714, following his earlier alcohol thermometer of 1709, and introduced the temperature scale that still bears his name in 1724.

Facts

Measures

Temperature. 1

Operating Principle

Different designs translate a physical property that changes predictably with temperature into a reading: thermal expansion of a liquid such as mercury, changing electrical resistance in a resistance thermometer, or a voltage generated by the thermoelectric effect in a thermocouple. 1

Resolution

Clinical thermometers are commonly readable to 0.1 degrees Celsius; mercury thermometers can achieve a measurement uncertainty of about plus or minus 0.01 degrees Celsius between 0 and 100 degrees Celsius; thermocouples typically carry an error of about plus or minus 0.5 to 1.5 degrees Celsius. 1

Operating Range

Mercury thermometers are typically used from about minus 38 to 350 degrees Celsius; thermocouples cover a wide range from cryogenic temperatures to over 1000 degrees Celsius; the International Temperature Scale of 1990 extends from 0.65 kelvin to about 1,358 kelvin. 1

Disputed

Invented Year

1714 2

Galileo's open thermoscope of about 1592 is the earliest device to register temperature change but had no fixed scale and vented to open air; Fahrenheit's sealed, scaled mercury thermometer of 1714 is the version usually credited as the first practical, reliable instrument.

Cross-Tradition Connections

Invented By

Daniel Gabriel Fahrenheit

Why this is disputed. The sealed mercury in glass thermometer with a standardized scale is credited to Fahrenheit in 1714; earlier open air thermoscopes without a standard scale existed from the early 1600s.

Source Thermometer (Britannica)

Galileo Galilei

Why this is disputed. Built an open thermoscope around 1592 to 93, the earliest known device to register temperature change, but it had no fixed scale and vented to open air, so it is a precursor rather than the practical instrument.

Source Thermometer (Britannica)