Home > Infrared Know How > Thermometry History
The History of Temperature and Thermometry

The realization that some things are hotter than others and that some are colder must have long preceded the concept of temperature in the history of human. Although ancient cooks and bakers, smelters and smiths, potters and ceramists don't know the distinction between heat and temperature, their works are involved in temperature. We can tell a toddler some things are too hot and others are too cold even we don't know the temperature.
Temperature may be said to derive from the recognition of the need to define these differences more precisely than by the positive, comparative and superlative of adjective hot and cold. Aristotle postulated his four qualities the hot, the cold, the moist, and the dry, set up a conception which endured for about two thousand years.
The ideas of Aristotle were adopted by Galen(A.D. 130-200),who was the first man to describe the heat and cold by a number about fifteen hundred years ago. And the word temperature originated from temper, after Galen determined the "complexion" of a person by the proportion in which above four qualities were tempered. [1].He gave the earliest notion of a standard of temperature, although the temperature meant the tempering of the qualities in a substance until the eighteenth century.
The temperature had a precise physical meaning today, temperature is the degree of sensible heat of a body. In other words, temperature is the hotness of a body - like the density of liquid or the brightness of a lamp.(Even more so, for today intensity of sound and light flux are expressed in CGS units).Unlike mass or length which are both extensive and additive, temperature is intensive. Temperature is an intensive and dimensionless magnitude-one of the few purely such in all natural phenomena. [2] In other definition, temperature can be considered to be the level of thermal energy. It is analogous to voltage as the level of electrical energy, or to elevation as the level of mechanical potential energy. Temperature is the driving force for heat flow, just as voltage is the driving force for fluid flow.[3]
The concept of temperature has been the most difficult of the common properties of matter to define clearly. It is helpful to review the historical development of temperature measurement because only after crude methods of temperature measurement were developed could the concept of temperature really be defined.

The History of Thermometry

The concept of temperature, as the scientific principles on which temperature measurement is based, evolved as a part of the development of the science.
The instrument by which the temperature of bodies is registered is called a thermometer or measurer of warmth, and the method of constructing and using thermometers may be called thermometry.[4]The history of thermometry was a part of history of science. The history will give us insights regarding the meaning of temperature and its measurement units, and will give us some background regards other concerns which need to be met.
The ancient Greek knew the expansion of air by heat long time ago. The earliest writings concerned that phenomena were the Works of Philo of Byzantium(II Cent. B.C.) and Heron of Alexandria. Due to the intercourse of culture, their works were translated into Arabic and Latin version.
And della Porta was an important disseminator, whose chief work Magia Naturalis( Natural Magic,1558,1589) not only included many classical antiquity and tradition, but also originated some experiments and contrivances. A simple air-thermoscope was described, which traps air in a bulb so that the air expands or contracts in response to a temperature increase or decrease, it moves a liquid column in a long tube (Fig. 1.1). Thermoscope is the not a thermometer but is its predecessor. the logical distinction between the two is that the thermometer possesses a scale, while a thermoscope does not.
The history of knowledge decided the earliest thermometer was the air thermometer after the air-thermoscope appeared. There were four inventors of thermometer at the first few years of the seventeenth century, they were Galileo, Sanitorio, Fludd and Drebbel.
It was said that Galileo was the first inventor of thermometer, but there was no work or document survived in which Galileo claimed his invention or made any question about priority, and he certainly gave little or no attention to the use and development of thermometer.
By modern standard the first physiologist Santorio Santorii (Sanctorius) of Padua would be regarded as the discoverer of the thermometer, for he published the earliest account of it in Part III of his commentaria in artem Medicinalem Galenis (Venice,1612),of which the Imprimatur is dated 1611.Santorio claimed he had adapted thermometer (Fig.1.2) from Heron. He used the instrument to estimate the heat of a patient's heart by measuring the heat of the expired air. His method of measurement was quite different from that of modern physicians. He measured the rate of change of the temperature of the thermometer by observing the distance through which the liquid fell during ten beats of a pulsilogium, a small pendulum. The result depended not only on the patient's temperature, but on the rapidity of his peripheral circulation. That was a fast indictor of fever because the ordinary thermometer took much longer to attain the temperature of normal person than that of a fever patient.

Fig.1.1 the first published figure of
thermoscope(published 1620),
Inventor was Santorio.[1]

Fig.1.2 The thermometer of Sanctorius
(1622,op. cit.,col. 22),
with pulsailogium on left.

Englishman Robert Fludd(1574-1651) also was regarded as one independent inventor of thermometer, he may have modified Philo's apparatus into the weather-glass but did not do so until some period between 1617 and 1626. Philo described an experiment to demonstrate the expansion of air by heat ,in which a tube from a hollow sphere was extended over a jug of water. If the sphere was placed in the sun, bubbles were released as air expanded out of the sphere. When moved to the shade, water rose in the tube as air in the sphere contracted(like left side of Fig. 1.3 ,but no scale on the tube). Fludd's contribution was to set the scale on the tube, and place the sphere vertically above the jug, converting ancient Philo's air-thermoscope to an air-thermometer.

The fourth inventor of thermometer was Drebbel, He made a two-bulbed J-shaped thermometer at any date between 1598 and 1622. (Fig.1.4), although Drebbel planned to construct a perpetuum mobile by the contraction or expansion of an enclosed air at the beginning.

Fig.1.3 The illustration of thermometer in the
Philosophia Moysaica(by Fludd,1638,p.2)

Fig.1.4 Drebbel Thermometers from Leurechon's Recreations
Mathematiques(facing p.90) Enlarged from 1626 edition.

One fault of the air-thermometer was they also responded to the change in atmospheric pressure. The effect was not known originally, as there was no concept of an atmospheric pressure. Two other problems, the lack of portability and evaporation of water, led to the development of sealed thermometers, namely the liquid-in-glass thermometer.
The sealed liquid-in-glass thermometer was invented by Ferdinand II,Grand Duck of Tuscany, in about 1654[note,1641 on "Temperature" by T.J Quinn], it used the thermal dilation of a liquid instead of air to sense temperature changes.[3]The volume of most substances increases continuously as the temperature rises, the liquid dilation was much less than that of air, the first liquid in the glass was spirits of wine, and the end of the tube was sealed with a flame(Fig.1.5). But this kind of thermometer met the problem of comparisons, which thermometer was the correct? Since there was no calibration some time until the people knew a fixed reference temperature in physical situation. Every thermometer craftsman produced a unique instrument. One can only make comparisons of temperature by using the same instrument, or perhaps with a nearly identical instrument made by the same craftsman.
One of the earliest attempts at calibration and standardization between thermometers was made in October 1663 in London. The members of Royal Society of London agreed to use one of several thermometers made by Robert Hooke as the standard so that the reading of others could be adjusted to it. Thus the reading in one laboratory could compare a temperature to reading in another laboratory through the standard correction.
The development of stable Fahrenheit thermometers was a watershed point in the development of thermometry. The methods of making scale were in confusion at that time, because the craftsman in different countries used different calibration points, there were 18 scales up to 1841. Daniel Gabriel Fahrenheit, a Danzig instrument maker learned the calibration of thermometer from Ole Romer, a Danish astronomer. Between 1708 and 1724, Fahrenheit begun producing thermometers, first with Romer's scale, then with a modified Romer scale, and finally with the Fahrenheit's scale, used today. Fahrenheit improved the precision of thermometer greatly after he made the bulb of thermometer a cylinder rather than a globe, substituted mercury for spirits because mercury had a more nearly linear thermal expansion with temperature. Many of his procedures for producing quality thermometers appeared to be trade secrets, it was fairly certain that he used the melting point of the mixture of sea salt, ice and water, the armpit temperature of a healthy man as calibration points(Fig.1.6)).When this scale was adopted by Great Britain, the temperature of 212?was established as the boiling point; this temperature and the ice point was used as the two fixed calibration points.
Following Fahrenheit's work, many scientists developed the practical scales based upon arbitrary fixed points, such as Celsius,,Daniell ,Becquerel.
In about 1740, Anders Celsius in Uppsala,Sweden, prosposed his centigrade scale, he had the boiling point of water at 0?, and the freezing point of water at 100?.The word "centigrade" means a scale that is divided into 100 parts. It's not clear that where and by whom the centigrade scale was invented, the centigrade scale means the "Celsius" scale now. Some believed that Carl Von Linne probably had suggested to Celsius the possibility of dividing the space between the ice point and steam point into 100 parts, Linnaeus inverted the scale to the scale we use today. It was in 1948 that the name of that scale has been the "Celsius" scale.

Fig1.5 Liquid-in-glass thermometer of
the Accademia del Cimento.

Fig1.6 Fahrenheit
thermometer in1850s.

Daniell had invented a pyrometer in 1825,when the future Lord Kelvin was a year old. Becquerel had used a platinum-vs-palladium thermocouple in 1826.
The branch of thermometry initiated by Fahrenheit led ,via mercury thermometer, platinum resistance thermometer and platinum-vs-palladium thermocouple toward the end of the nineteenth century[5]. We'll see the culminating result of practical thermometry the International Temperature Scale of 1990(ITS-90) in the Chapter 2.
But the practical thermometry cannot tell the precise meaning of temperature, and the size of the degree, the unit for measuring temperature, was completely arbitrary. The two primary degree units in use today were based on the original centigrade and Fahrenheit scales. There are 180 degrees between the ice point and the boiling point on the Fahrenheit scale, and 100 degrees for the same interval on the centigrade scale. So the Fahrenheit degree is smaller and 1 degree centigrade(now Celsius) equals 1.8 degrees Fahrenheit, so the practical temperature scale depends on the properties of some bodies
Another branch of thermometry is the gas thermometry and thermodynamic thermometry.
Before Fahrenheit thermometer appeared, Robert Boyle reported on his study of air trapped in a U tube in 1660,he found that the volume at constant pressure was a function of temperature. While Fahrenheit studies his liquid-in-glass thermometer, the French scientist Amontons developed the constant volume gas thermometer. He used air as the thermometric medium, and concluded that the lowest temperature which could exist would correspond to a zero gas pressure. This must have been the first step on the way to an understanding of the concept of temperature. According to Amontons we could define the temperature as being simply proportional to the pressure of a gas, and thus we would need only one fixed point to define a scale[5]. But the new temperature scale didn't appear at that time, maybe because of the cumbersome operation of gas thermometer. Jacques-Alexandre Charles studied the phenomena again in 1787.Jaspeh L. Gay-Lussac extended Charle's work, all his gases-air, oxygen, nitrogen, hydrogen, and carbon dioxide-expanded the same amount when heated from the ice point to the boiling point. The result showed that at constant pressure, and the =1/267 (degree)-1 is the mean volumetric coefficient of thermal expansion. In 1847,Victor Regnault obtained a better value of 1/273. Later experiments revealed that all gas had a very slightly different thermal coefficients, however all were found to approach a common value 1/273.15degC as the pressure approached zero. The gases that obey the temperature-volume relationship exactly at constant pressure (and the pressure-volume relationship exactly at constant volume) were defined the perfect (or "ideal" or "simple") gas. In fact,all gases at extremely low pressure approach perfect gas behavior. The volume of the perfect gas in the gas thermometer will approach zero as t= -273.15 because at constant pressure. We can establish a new zero of temperature at the ice point -273.15 , namely the absolute zero degree. And the perfect gas temperature scale T= t+273.16 was defined in 1954. The gas thermometer is now rarely used directly in practical work for the measurement of temperatures, owing to the complications that would be involved consequently to realize the gas scale it is necessary to transfer the scale to auxiliary standards, that is the above empirical temperature scale.[6]
The precise meaning of temperature came after the Kelvin's thermodynamic temperature appeared. In 1824, Carnot had laid down his principle of reversibility with regard to "quantity of heat" in an ideal "body" that "undergoes changes" and in 1845(after 30 years of experiments)Joule demonstrated mechanical equivalence. Heat now became an engineering "quantity", measurable in foot-pounds. But what was temperature? The explanation seems so near, but look here " the higher the temperature the greater the quantity of heat in Carnot's "body". If we can't ever know what temperature is ,can we at least establish its real relation to heat independently of the actual behavior of mercury, or of a gas and yet in such a way that we can make the thermometers that agree with one another?[1] By the first law and the second law of thermodynamic law, it is a stand proof that for a reversible heat engine operating over a Carnot cycle between two temperature and ,the ratio of the heat taken in at the higher temperature to that given out at the lower temperature is proportional simply to the ratio of the same function of each of the two temperatures. . where is a function only of ,and is the same function only of ,independent of the particular properties of the working fluid. William Thomson(later Lord Kelvin) realized,1n 1848,that this relation could be used to define the ration of any two temperatures. The values of the temperatures would depend upon the functional form ,but by taking the simplest possible form of the function he defined a temperature, which he called thermodynamic temperature, T ,by the relation .Thermodynamic temperature thus has the property that ratios of T are defined in terms of the properties of reversible heat engines and are independent of the working substance. The definition of the quantity thermodynamic temperature then has to be completed by assigning a particular numerical value to an arbitrary fixed point of temperature, triple point of the water. So the real meaning of the temperature is a physical quantity which is fundamental for the field of thermodynamic and is directly related to the basic laws of thermodynamics.[5]
In principle ,any suitable thermodynamic equation may be used as the basis for a thermometer, such as Acoustic thermometer, thermal noise thermometer, gas thermometer, radiation thermometer, etc.
However, with the exception of the radiation thermometers used at high temperature, thermodynamic thermometers cannot arrive the highest precision desired, and are complex and time consuming to use. To overcome these difficulties, the above empirical temperature scale was defined as ITS by (CIPM) under the convention du Metre,the founding treaty for the SI,and was regularly revised with the current version agreed to in 1990,and known as ITS90. The ITS are empirical temperature scales giving a close approximation to the known thermodynamic scale, but are more precise and easier to use. Now all temperature measurement should be traceable to the current ITS.

[1]M. F. Behar ,Temperature and Humidity measurement and control ,Instruments publishing company,113-122, (1932)
[2] F. Sherwood Taylor, The origin of the thermometer , Annals of Science, Vol.5, 129-156
[3]Thomas D. McGee ,Principles and Methods of Temperature Measurement,1988
[4] J. Cleak Maxwell,Theory of Heat,1916
[5] T.J. Quinn,Temperature,1990
[6] EZER,Griffiths,Charles ,Method of Measuring temperature,1947

Founded in July 2000, ZyTemp belongs to world-class Infrared Technology-oriented thermometer manufacturer - Radiant Innovation Inc. and become a premier provider of infrared temperature measurement devices. Originally started from a professional team of engineers specializing in infrared thermometry, this company is now emerging as worldwide well-known manufacturer of infrared thermometers (IRT).
Copyright (c) 2000-2017 RADIANT INNOVATION INC.
All Rights Reserved.