, who pioneered the idea of an absolute zero. One of the first to discuss the possibility of an absolute minimal temperature was
Robert Boyle. His 1665
New Experiments and Observations touching Cold, articulated the dispute known as the
primum frigidum. The concept was well known among naturalists of the time. Some contended an absolute minimum temperature occurred within earth (as one of the four
classical elements), others within water, others air, and some more recently within
nitre. But all of them seemed to agree that, "There is some body or other that is of its own nature supremely cold and by participation of which all other bodies obtain that quality."
Limit to the "degree of cold" The question of whether there is a limit to the degree of coldness possible, and, if so, where the zero must be placed, was first addressed by the French physicist
Guillaume Amontons in 1703, in connection with his improvements in the
air thermometer. His instrument indicated temperatures by the height at which a certain mass of air sustained a column of mercury—the pressure, or "spring" of the air varying with temperature. Amontons therefore argued that the zero of his thermometer would be that temperature at which the spring of the air was reduced to nothing. He used a scale that marked the boiling point of water at +73 and the melting point of ice at +, so that the zero was equivalent to about −240 on the Celsius scale. Amontons held that the absolute zero cannot be reached, so never attempted to compute it explicitly. The value of −240 °C, or "431 divisions [in Fahrenheit's thermometer] below the cold of freezing water" was published by
George Martine in 1740. This close approximation to the modern value of −273.15 °C Values of this order for the absolute zero were not, however, universally accepted about this period.
Pierre-Simon Laplace and
Antoine Lavoisier, in their 1780 treatise on heat, arrived at values ranging from 1,500 to 3,000 below the freezing point of water, and thought that in any case it must be at least 600 below.
John Dalton in his
Chemical Philosophy gave ten calculations of this value, and finally adopted −3,000 °C as the natural zero of temperature.
Charles's law From 1787 to 1802, it was determined by
Jacques Charles (unpublished),
John Dalton, and
Joseph Louis Gay-Lussac that, at constant pressure, ideal gases expanded or contracted their volume linearly (
Charles's law) by about 1/273 parts per degree Celsius of temperature's change up or down, between 0° and 100° C. This suggested that the volume of a gas cooled at about −273 °C would reach zero.
Lord Kelvin's work After
James Prescott Joule had determined the mechanical equivalent of heat,
Lord Kelvin approached the question from an entirely different point of view, and in 1848 devised a scale of absolute temperature that was independent of the properties of any particular substance and was based on
Carnot's theory of the Motive Power of Heat and data published by
Henri Victor Regnault. It followed from the principles on which this scale was constructed that its zero was placed at −273 °C, at almost precisely the same point as the zero of the air thermometer, High-precision gas thermometry in the 1930s further narrowed the value. In 1937, Masao Kinoshita and Jiro Oishi reported measurements of expansion and pressure coefficients for nitrogen, hydrogen, helium, and neon, deriving the absolute temperature of . The Tokyo Tech Museum and Archives later identified Kinoshita and Oishi's measurements, which gave a value close to 273.15 K for the ice point, as part of the experimental basis for the value adopted in 1954 thermometry discussions.
The race to absolute zero With a better theoretical understanding of absolute zero, scientists were eager to reach this temperature in the lab. By 1845,
Michael Faraday had managed to liquefy most gases then known to exist, and reached a new record for lowest temperatures by reaching . Faraday believed that certain gases, such as oxygen, nitrogen, and
hydrogen, were permanent gases and could not be liquefied. Decades later, in 1873 Dutch theoretical scientist
Johannes Diderik van der Waals demonstrated that these gases could be liquefied, but only under conditions of very high pressure and very low temperatures. In 1877,
Louis Paul Cailletet in France and
Raoul Pictet in Switzerland succeeded in producing the first droplets of
liquid air at . This was followed in 1883 by the production of liquid oxygen by the Polish professors
Zygmunt Wróblewski and
Karol Olszewski. Scottish chemist and physicist
James Dewar and Dutch physicist
Heike Kamerlingh Onnes took on the challenge to liquefy the remaining gases, hydrogen and
helium. In 1898, after 20 years of effort, Dewar was the first to liquefy hydrogen, reaching a new low-temperature record of . However, Kamerlingh Onnes, his rival, was the first to liquefy helium, in 1908, using several precooling stages and the
Hampson–Linde cycle. He lowered the temperature to the boiling point of helium . By reducing the pressure of the liquid helium, he achieved an even lower temperature, near 1.5 K. These were the
coldest temperatures achieved on Earth at the time and his achievement earned him the
Nobel Prize in 1913. Kamerlingh Onnes would continue to study the properties of materials at temperatures near absolute zero, describing
superconductivity and
superfluids for the first time. ==Negative temperatures==