Rectal thermometer

A medical thermometer is used for measuring human or animal body temperature. The tip of the thermometer is inserted into the mouth under the tongue (oral or sub-lingual temperature), under the armpit (axillary temperature), or into the rectum via the anus (rectal temperature).

The medical thermometer began as an instrument more appropriately called a water thermoscope, constructed by Galileo Galilei circa 1592–1593. It lacked an accurate scale with which to measure temperature and could be affected by changes in atmospheric pressure.

Italian physician Santorio Santorio is the first known individual to have put a measurable scale on the thermoscope and wrote of it in 1625, though he possibly invented one as early as 1612. His models were bulky, impractical and took a fair amount of time to take an accurate oral reading of the patient's temperature.

There are two particular men who switched out water for alcohol in the thermometer. The earliest is Ferdinando II de' Medici, Grand Duke of Tuscany (1610–1670), who created an enclosed thermometer that used alcohol circa 1654.Daniel Gabriel Fahrenheit (1686–1736), a Polish-born German physicist, engineer, and glass blower, made contributions to thermometers as well. He created an alcohol thermometer in 1709 and later innovated the mercury thermometer in 1714. Mercury, he found, responded more quickly to temperature changes than the previously used water. Fahrenheit also created the temperature scale which is named after him, having recorded the system in 1724. The scale is still only mainly used for everyday applications in the United States, its territories and associated states (all served by the U.S. National Weather Service) as well as the Bahamas, Belize, and the Cayman Islands.

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