When Was the Thermometer Invented?
The first practical thermometer or instrument for measuring temperature was invented shortly before the end of the 16th Century by the famous Italian astronomer Galileo. It was an air thermometer giving only a rough indication of the degrees of heat and cold, and later he increased its efficiency by using alcohol instead of air.
The principle on which most thermometers work is that a liquid or gas used for measuring expands or contracts with changes in temperature more rapidly than the glass containing it. Thus when a colored liquid is confined in a thin glass tube the difference in expansion, as shown by the level of the liquid against a graduated scale, indicates the temperature.
About 1714 the German scientist Gabriel Daniel Fahrenheit designed a thermometer which, for the first time, used mercury as the measuring agent. He also introduced the scale named after him in which (32°) is the freezing point of water and (212°) the boiling point. Mercury is still used in most thermometers because it has a high boiling point (674°) and a low freezing point (-38°).
An alcohol thermometer, still in use in some countries, was made by René de Réaumur, a French naturalist, about 1731. About 11 years later Anders Celsius, a Swedish astronomer, used the centigrade scale for the first time, with freezing point (0°) and boiling point at (100°).
The word thermometer (in its French form) first appeared in 1624 in La Récréation Mathématique by J. Leurechon, who describes one with a scale of 8 degrees. The word comes from the Greek words θερμός, thermos, meaning “hot” and μέτρον, metron, meaning “measure”.
In about 1654 Ferdinando II de’ Medici, Grand Duke of Tuscany (1610–1670), made sealed tubes part-filled with alcohol, with a bulb and stem; the first modern-style thermometer, dependent on the expansion of a liquid, and independent of air pressure. Many other scientists experimented with various liquids and designs of thermometer.
However, each inventor and each thermometer was unique—there was no standard scale. In 1665 Christiaan Huygens (1629–1695) suggested using the melting and boiling points of water as standards, and in 1694 Carlo Renaldini (1615–1698) proposed using them as fixed points on a universal scale.
In 1701, Isaac Newton (1642–1726/27) proposed a scale of 12 degrees between the melting point of ice and body temperature. Finally in 1724, Daniel Gabriel Fahrenheit (1686–1736) produced a temperature scale which now (slightly adjusted) bears his name. He could do this because he manufactured thermometers, using mercury (which has a high coefficient of expansion) for the first time and the quality of his production could provide a finer scale and greater is reproducibility, leading to its general adoption.
In 1742, Anders Celsius (1701–1744) proposed a scale with zero at the boiling point and 100 degrees at the freezing point of water, though the scale which now bears his name has them the other way around.
The first physician that put thermometer measurements to clinical practice was Herman Boerhaave (1668–1738). In 1866, Sir Thomas Clifford Allbutt (1836–1925) invented a clinical thermometer that produced a body temperature reading in five minutes as opposed to twenty. In 1999, Dr. Francesco Pompei of the Exergen Corporation introduced the world’s first temporal artery thermometer, a non-invasive temperature sensor which scans the forehead in about two seconds and provides a medically accurate body temperature.