|A circa 240BC Philo thermometer, the world's first thermometer. |
In circa 240BC, Philo of Byzantium (c.280-220BC) made the first thermometer-like devices.  Philo published a manuscript describing an experiment in which a tube from a hollow sphere was extended over a jug of water operating such that if the sphere was placed in the sun, bubbles would be released as air expanded out of the sphere; conversely, when moved into the shade, water rose in the tube as air in the sphere contracted, as pictured adjacent. 
In c.50AD, Hero of Alexandria (c.10-70AD) is said to have modeled is thermometer work on Philo, which he described in his Pneumatica. . Later, others, such as German engineer Robert Fludd, had access to Philo’s manuscript, and Galileo read Hero's Pneumatics in 1589. 
In 175AD, Galen made a crude thermometers was a nine-degree scale. In particular, Galen considered boiling water to be the hottest body, ice to be the coldest, and a mixture of equal parts ice and boiling water to be the neutral body. He then installed four degrees above and four degrees below the neutral point, thus making a nine-point scale. 
Sometime towards the later 16th century, Italian physician Santorio Santorio (1561-1636), a colleague of Galileo, is said to have made a thermoscope type of device, a type of redesigned Galen thermometer. In this sense, Santorio is often credited with the design of the clinical thermometer. 
In 1592, Italian scientist Galileo Galilei invented what most consider the first true thermometer.  It was described, according to a retrospect description by Galileo’s friend Benedetto Castelli, many years later, as such: 
“Galileo took a glass about the size of a small hen’s egg, fitted to a tube the width of a straw, and about two spans long: he heated the glass bulb in his hands and turned the glass upside down so that the tube dipped in water held in another vessel; as soon as the ball cooled down, the water rose in the tube. This instrument he used to investigate degrees of heat and cold.”
This device seems to have come to have been referred to as a ‘thermoscope’ (a thermometer without a scale), in modern discussion. Galileo’s instrument was said to depend on the observation that air expands when it is hot and contracts when it is cool. The water, differed in respect to mercury in a modern thermometer, serving merely to indicate the expansion or contraction of the air in the bulb. The preliminary heating was a trick to bring the water to a level where it could be seen. 
|Left: A circa 1610 Santorio thermoscope.  Center: Giuseppe Biancani’s 1617 thermoscope.  Right: Robert Fludd's 1638 air thermometer. |
In the 1613 words of his student Francesco Sagredo, who used Galileo's device for measuring the difference in temperature between air, snow, and ice, what Galileo had invented was an "an instrument for measuring heat", which can be said to be the first recorded definition of a thermometer.  Sagredo used the device to compare the temperature of lakes of different sizes as they cooled in the winter, finding that smaller ones cooled faster than larger ones. He recorded his readings as “degrees of heat”. 
In circa 1612 to 1624, Padua physician Sanctorius was the first to take a patients temperature, with some type of device, and to realize that a thermometer could work to give information useful in diagnosis. 
In 1638, in dependent of Galileo, English physician Robert Fludd used a modified Philo-thermometer design, in which he placed the sphere vertically above the jug (adjacent), thus making an unsealed air thermometer, with a scale. 
In the 1640s, German engineer Otto Guericke built a 20-foot high thermometer of sorts consisting of an expansion of alcohol in which a float, connected to a pointing angel, moved, thus indicating divisions graduated from “great heat” to “great cold”. 
In 1663, Jesuit Father Leuréchon coined the term “thermometer” from an earlier 1624 French term thermomètre, from Greek thermos "hot" + metron "measure". 
In 1654, or before, Italian scientist Ferdinand II, Grand duke of Tuscany, invented the sealed-glass thermometer. The devise was filled to a certain height with colored alcohol; then sealed by melting the glass tip; then marked off with 360 divisions, like the gradations of a circle, after which scientists began calling such divisions by the name “degrees”.  In this device, small glass bubbles filled with air at varying pressures hovered within the liquid, changing positions as the temperature rose or fell. These were called "spirit thermometers", because they were filled with "spirit of wine" (distilled alcohol) or "Florentine thermometers" (Florence being the capital of Tuscany). Scientists such as Robert Boyle, Robert Hooke, and Christopher Wren all used Florentine thermometers.
In 1664, English scientist Robert Hooke, a student of sorts of Guericke's work, a had made a variety of spirit thermometers, and notably used the bulb immersed in ice water as the zero mark on the thermometer, then made further marks on the tube to represent an expansion of 1/500th of volume of the fluid in the bulb.  Hooke was among the first to argue that the freezing point of water should be used as a fixed reference point.
In 1670, English chemist Robert Boyle, Hooke’s employer, used the term temperature to mean ‘degree of heat or cold’. 
In 1694, Padua mathematician Carlo Renaldini suggested the melting point of ice and the boiling point of water as the standard two main temperature set-points, the space between them on the thermometer stem being divided into twelve parts. 
In circa 1695, French physicist Guillaume Amontons designed a sealed-glass air-based thermometer.
In circa 1700, English physicist Isaac Newton designed a linseed-oil thermometer, publishing the results of experiment anonymously in the 1701 Transactions of the Royal Society.
In 1701, Danish astronomer Ole Romer invented a thermometer in which he defined the lower fixed point to be the freezing point of water at precisely 7.5 degrees and the upper point as the boiling point of water at 60 degrees. 
In circa 1708, it is said that Polish physicist Daniel Fahrenheit learned of Romer's scale during a visit with him. Fahrenheit commented in a retrospect letter to Dutch chemist Herman Boerhaave, that in about 1717 he had begun using an improved Romer scale, supposedly, by increasing the number of divisions by a factor of four, using different fixed points. Fahrenheit used the fixed points of 96 (instead of 22.5 or 90), the temperature of his wife's armpit, 32 the temperature of ice melting in water, and 0 the temperature of a bath of ice melting in a solution of common salt. This scale is now known commonly as the Fahrenheit temperature scale (˚F), which found its finalized form by 1724.
In 1730, French scientist Rene Reaumur (1683-1757) popularized a scale, supposedly a duplication of Hooke’s scale, in which the freezing and boiling point are set at 0 and 80 degrees, respectively.
|Galileo''s student Italian physicist Evangelista Torricelli (c.1635) holding what appears to be a Galilean-type thermometer. |
In 1726, Swedish instrument maker Daniel Ekstrom (1711-1755) had made thermometers on which the freezing point of water was 0˚ and the boiling point was 100˚.
In 1741, Swedish astronomer Anders Celsius (1701-1744) obtained a thermometer from St. Petersburg and etched on the side opposite its scale a formulation: a boiling point of 0˚ and a freezing point of 100˚. Celsius had proposed the downward counting scale in attempts to avoid negative numbers, of boiling water (0) and melting ice (100). Celsius published the findings of his scale in the 1742 paper “Observations of Two Persistent Degrees on a Thermometer”.
In 1750, Marten Stromer (1707- 1770), the successor to Celsius at Uppsala University, made a centigrade scale, on which he simply reversed Celsius' scale, putting 100 at the top and 0 at the bottom.
In 1758, Swiss botanist Carl Linnaeus claimed, its seems incorrectly, to have been the originator of the centigrade scale.  Linnaeus was Celsius’ assistant and in the years to follow Celsius’ death, encouraged the use of Celsius' scale among thermometer manufacturers, and also reversed Celsius’ scale to make his own patented “Linnaeus thermometer”, for use in greenhouses. 
At the 1948, International Conference on Weights and Measures, the scale “degrees centigrade” was renamed as “degrees Celsius”, in honor of Anders Celsius.
In 1848, the absolute temperature scale was conceived by Scottish physicist William Thomson, in his “On an Absolute Thermometric Scale founded on Carnot’s Theory of the Motive Power of Heat, and Calculated from Regnault’s Observations”, upon whom the unit of thermodynamic temperature, degrees kelvin (˚K), is named. 
|A depiction of a quantum thermometer (Ѻ), namely: an electron micrograph of the silicon nitride beam. The bottom shows how the beam deforms as it vibrates (length scale greatly exaggerated) with the red regions showing the most deformation, and the blue regions not moving at all. Over one vibrational period the center of beam goes from being stretched out as shown, to being compressed inward, and then back.|
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