The history of temperature stretches back for thousands of years. Temperature has always been an important and essential part of daily life and society, ever since bakers and blacksmiths relied on temperature to control chemical reactions.
Nowadays, temperature is better understood than ever, and a wide range of temperature-measuring equipment – thermoscopes, thermocouples and many types of thermometer – is necessary to measure and to help control it.
This blog series hopes to open your eyes about the history of temperature measurement, from the ancient through to the modern day. Enjoy!
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| The Fludd Thermometer (Photo sourced from: http://www.kumc.edu/) |
The invention of the first true thermometer is generally credited to Robert Fludd (1574 – 1637 A.D.), an English Paracelsian physician, astrologer, and mystic. Although the first detailed diagram of a thermoscope was created by Giuseppe Biancini (1566 – 1624 A.D.), an Italian Jesuit astronomer and mathematician, it was Robert Fludd who produced the first diagram of a true thermometer with both a temperature sensor and a scale.
The first person who developed the idea of the thermometer and actively used it was Santorio Santorio (1561 – 1636 A.D.), an Italian physiologist, physician and professor. He developed a clinical thermometer for use in his experiments at the University of Padua, and claimed to have produced it by adapting the design from Heron of Alexandria’s thermoscope. Santorio Santorio used his thermometer to produce an estimated heat of a patient’s heart by measuring the heat of his expired air.
All these early thermoscopes and thermometers had the same design flaw. They were all sensitive to air pressure as well as temperature, and therefore also functioned as barometers rather than as pure thermometers. The first thermometer which gave a clear reading of temperature, unaffected by any other factor, was invented by Ferndinando II de’Medici in 1654.
Medici (1610 – 1670 A.D.), Grand Duke of Tuscany, created the first modern thermometer, and the blueprint for many successive thermometer manufacturers. This was a sealed tube partially filled with alcohol, with a bulb and a stem. Because the tube was sealed, air pressure no longer affected the movement of the alcohol up or down the stem, leaving temperature as the only thing which was measured.
However, there was still one big problem in the thermometer industry. Every thermometer manufacturer had his own scale and his own system for measuring temperature. The scales and measurements were not standardised or calibrated to one another.
An early attempt at encouraging the use of a universal scale was in October 1663. The Royal Society in London proposed the use of one of Robert Hooke’s many thermometer scales as standard in the industry (Hooke was an English natural philosopher, architect and inventor).
Still, the Royal Society had no real power to implement its recommendation, and a variety of thermometers and measures remained in use. Slowly a scale evolved: Christian Huygens in 1665 suggested the melting and boiling points of water as standard lower and upper limits, and in 1701 Isaac Newton proposed a scale of twelve degrees, with the extremes being melting ice and body temperature.
Eventually, it was market forces which decided which thermometer scale would become standard use. Ole Christiansen Romer (1644 – 1710 A.D.), the royal mathematician of Denmark and a noted astrologer, created a scale where the upper limit was body temperature (the temperature of a healthy adult male’s armpit), and the lower limit a mixture of salt and ice. This is known as a ‘frigorific’ mixture: two materials whose temperatures can vary, but which always produce the same temperature when mixed together.
However, it was when Daniel Gabriel Fahrenheit visited Romer in 1708, and started using his scale in 1724, that it really caught on. Fahrenheit (1686 – 1738 A.D.), a German physicist and engineer, was the first thermometer manufacturer to make his thermometers with mercury instead of alcohol.
Mercury is a better substance to use because its movement corresponds more exactly to temperature change, and so a thermometer containing it can produce a more accurate reading than a thermometer using alcohol. So Fahrenheit’s thermometers became the most popular designs, and eventually the standard ones. Because those buying the thermometers had to use the scale with which they came equipped, his scale eventually became the standard one as well, and still bears his name today.
Fahrenheit wanted a scale which was divisible by twelve, and so he called his upper point (body temperature) 96 degrees. As body temperature varies, the upper limit of the Fahrenheit scale was later changed to the temperature of boiling water, which was said to be 212 degrees. Nowadays, the Fahrenheit scale is only used widely in the United States of America and a few other countries (for example, Belize). The scale most widely used in thermometers of all kinds is the Celsius scale.
The Celsius scale was developed by Anders Celsius (1701 – 1744 A.D.), a Swedish astronomer who devised a scale of 100 degrees, with zero as the boiling point of water and 100 as its freezing point. He set this scale out in his paper ‘Observations of two persistent degrees on a thermometer’ in 1742. As he died just two years later, his assistant Carolus Linnaeus was instrumental in developing and publicizing the scale, and in encouraging its use among thermometer manufacturers.
Linnaeus reversed the scale, making zero the freezing point of water and 100 its boiling point, and used it in his patented linnaeus-thermometers, which were thermometers for use in greenhouses.
The scale caught on, with the endorsement of such figures as Daniel Ekstrom, Sweden's leading instrument-maker at the time, and Pehr Elvius, the secretary of the Royal Swedish Academy of Sciences. Since about 1950, the ‘centigrade’ scale (officially named the Celsius scale in 1948) has been the most widely used thermometer scale worldwide, and is used in thermometers of all kinds and in all industries, with the exception of some scientific fields (e.g. astrophysics or low-temperature research) where the specialised Kelvin scale is used instead.
Next in this series of posts, learn about the explosion of thermometer development that occurred in the 20th century.
