Inventing Temperature

by Hasok Chang

  Boyle's law, or Mariotte's law. A regularity attributed to Robert Boyle or Edme Mariotte, which states that the product of pressure and volume is constant for a body of gas at constant temperature (pv = const.).

  Bumping (soubresaut in French). A noisy and unstable type of boiling, in which large isolated bubbles of vapor rise occasionally, either one at a time or severally in an irregular pattern. The temperature is unstable, dropping when the large bubbles are produced and rising again while no bubbles form.

  Caloric. The material substance of heat. The term was coined by Antoine-Laurent Lavoisier as part of his new chemical nomenclature in the 1780s. Although the majority of chemists and physicists at the time agreed that heat was a material substance and many people used the term "caloric," there were considerable differences among the various theories of caloric. Cf. chemical caloric theory; Irvinism.

  Calorimetry. The quantitative measurement of the amounts of heat. The most common methods in the eighteenth and nineteenth centuries were ice calorimetry and water calorimetry.

  Cannon-boring experiment. The experiment in which Count Rumford (Benjamin Thompson) showed that a great deal of heat was generated in the process of grinding through a metal cylinder with a blunt borer. Rumford first noticed the heat generated by such friction while supervising the boring of cannons in the Munich arsenal, when he was charged with running the Bavarian army. Contrary to later legend, this experiment did not make a convincing refutation of the caloric theory, although it was well known and widely debated.

  Cardinal scale. A scale of measurement that assigns numbers that are suitable for arithmetic operations. Cf. ordinal scale.

  Carnot engine, Carnot cycle. The ideal and abstract heat engine first conceived by Sadi Carnot. See the section "William Thomson's Move to the Abstract" in chapter 4 for a full explanation.

  Centigrade scale, Celsius scale. The centigrade scale is the common scale in which the freezing/melting point of water was defined as 0° and the boiling/steam point of water as 100°. This is commonly attributed to Anders Celsius, but his original scale, although centigrade, had the boiling point as 0° and the freezing point as 100°. There are disputes about who first conceived the centigrade scale with its modern direction of numbers.

  Change of state. See states of matter.

  Charles's law, or Gay-Lussac's law. A regularity attributed to J. A. C. Charles or Joseph-Louis Gay-Lussac, which states that the volume of a gas under fixed pressure varies linearly with temperature.

  *Chemical caloric theory. The tradition of caloric theory, most clearly originating from Antoine-Laurent Lavoisier but also Joseph Black, in which caloric was conceived as a substance capable of combining chemically with other substances (see combined caloric).

  Coherentism. An epistemological standpoint according to which a belief is justified insofar as it belongs to a system of beliefs that are mutually supportive. Coherentists deny that any beliefs are self-justifying. Cf. foundationalism.

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  Combined caloric. In chemical caloric theory, caloric in the state of chemical combination with ordinary matter (cf. free caloric). In more phenomenological terms, combined caloric would be described as latent heat. Antoine-Laurent Lavoisier explained the heat in combustion as the release of combined caloric from oxygen gas.

  Comparability. The requirement that a good measuring instrument should be self-consistent. When the instrument is taken as a type, comparability means that all instruments of the same type should agree with each other when applied to a given situation. This requirement is based on the principle of single value. Victor Regnault used comparability as his chief criterion for testing the correctness of thermometers.

  Delisle (de l'Isle) scale. The temperature scale created by Joseph-Nicolas Delisle, French astronomer in Russia. Its zero-point was set at the boiling point of water, and the numbers increased with increasing cold, with the freezing point of water designated as 150°.

  Duhem-Quine thesis. See holism.

  Dulong and Petit's law, or law of atomic heat. The empirical observation made by Pierre Dulong and Alexis-Thérèse Petit that the product of atomic weight and specific heat (by weight) was roughly the same for all chemical elements. This was often taken to mean that an atom of any element had the same capacity for heat; hence the law was sometimes referred to as the law of "atomic heat."

  Dynamic theory of heat, or mechanical theory of heat. Any theory of heat in which heat is conceived as a form of motion (cf. material theory of heat).

  Ebullition. Generally, just another word for boiling. However, for Jean-André De Luc, "true ebullition" was a theoretical concept that designated the boiling that took place purely as an effect of heat, as opposed to ordinary boiling, which took place at a lower temperature because of the action of the air dissolved in water.

  École Polytechnique. The elite technical university in Paris, founded in 1794 as part of the educational reforms of the French Revolution. A majority of leading French physical scientists in the first half of the nineteenth century taught or studied there.

  *Epistemic iteration. A process in which successive stages of knowledge, each building on the preceding one, are created in order to enhance the achievement of certain epistemic goals. It differs crucially from mathematical iteration in that the latter is used to approach a correct answer that is known, or at least in principle knowable, by other means.

  Expansive principle. James Watt's maxim that higher efficiency in a steam engine can be obtained if one allows steam to do work through expanding by its own power.

  Fahrenheit scale. The popular temperature scale devised by Daniel Gabriel Fahrenheit, in which the freezing point of water is set at 32° and the boiling point of water at 212°. Fahrenheit's motivation in arriving at such a scale was complicated; see Middleton 1966 for a full account.

  Fixed point. A reference point in a thermometric scale, which is given a fixed value by definition. The term is also used to refer to the natural phenomenon that defines such a point.

  Foundationalism. The doctrine that epistemic justification has a hierarchical structure. According to foundationalism, some beliefs are self-justifying and as such constitute one's evidence base; others are justified only if they are appropriately supported by these basic beliefs. Cf. coherentism.

  Free caloric. In chemical caloric theory, caloric that is not bound up in chemical combination with ordinary matter (cf. combined caloric). In more phenomenological terms, free caloric would be described as sensible heat.

  Free caloric of space. Pierre-Simon Laplace's term to describe the caloric that was postulated to exist in intermolecular spaces. Such caloric was understood to be in the process of radiative transfer between molecules. Laplace defined temperature as the density of free caloric of space.

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  Free surface. A surface at which a change of state can occur. In John Aitken's view, a change of state did not necessarily take place when the temperature associated with it was reached; only the presence of a free surface enabled the change.

  Freezing mixture. A mixture used to obtain very low temperatures. Generally it consisted of an acid mixed with ice (or snow). Freezing mixtures were used for a long time without any satisfactory theoretical understanding of their workings. With the advent of Joseph Black's concept of latent heat, it was understood that the addition of the acid melted the ice by lowering its freezing point, and the ice absorbed a great deal of heat from the surroundings in the process of melting.

  Freezing point. The temperature at which a liquid freezes. In the context of thermometry, an unspecified "freezing point" usually refers to the freezing point of water. The question of the fixedness of the freezing point of a pure liquid is complicated by the phenomenon of supercooling. And although the freezing point of water is commonly considered to be the same as the melting point of ice, there have been doubts on that question.

  Heat capacity. The capacity of a material object for containing heat. Operationally the heat capac
ity of a body is identified as the amount of heat required to raise its temperature by a unit amount, which is specific heat. In Irvinist caloric theory heat capacity and specific heat were explicitly identified. In the chemical caloric theory, however, the identification was denied, since it was considered possible that caloric could become combined (latent) as it entered a body, hence not affecting the thermometer at all. In modern thermal physics the concept of heat capacity is not considered cogent, although in common discourse the term is still often used to mean specific heat.

  Hissing (sifflement in French). The pre-boiling phenomenon in which numerous bubbles of vapor rise partway through the body of water, but are condensed back into the liquid state before they reach the surface. This happens when the middle or upper layers of the water are cooler than the bottom layers. The familiar noise from a kettle before full boiling sets in is due to hissing.

  Holism (in theory testing). The view, attributed most famously to Pierre Duhem and W. V. O. Quine, that it is impossible to subject an isolated hypothesis to an empirical test. Rather, only a sizeable group of hypotheses can have empirical significance and be subjected to empirical tests. Cf. auxiliary hypotheses.

  Hypothetico-deductive (H-D) model of theory testing. According to the H-D model, the testing of a theory consists in deducing an observable consequence from it, which can then be compared with actual observations. All empirical theories are hypothetical and can be tested this way.

  Ice calorimetry. The measurement of the quantity of heat through the melting of ice. A hot object is introduced into a chamber surrounded by ice at the melting point, and the amount of heat given from the hot object to the ice is calculated as the product of the weight of melted water and the latent heat of fusion by weight. The idea was first put into practice by Pierre-Simon Laplace and Antoine-Laurent Lavoisier.

  Ideal gas, ideal gas law. The "ideal gas" has been conceived in various ways. The standard calorist conception was that gases came close to exhibiting the pure effect of caloric, since they contained a great deal of caloric and the molecules of ordinary matter were separated so far from each other that the attractions between them became negligible. It was easy to imagine an ideal gas in which that negligible intermolecular interaction vanished altogether; in such a case the thermal expansion of gases was imagined to be perfectly regular. In the kinetic theory of gases, the ideal gas was conceived as one in which the molecules were not only noninteracting (except by mutual collision) but pointlike (occupying no space) and perfectly elastic. It was seen that such an ideal gas would obey the ideal gas law, commonly written as PV = RT, where R is a constant. The ideal gas law could be considered a synthesis of Boyle's law and Charles's law.

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  *Idealization. A description in which some properties of an object are set at certain values that are convenient or desirable, though not actually obtained. Idealization is not to be confused with abstraction.

  Irvinist caloric theory (Irvinism). The influential caloric theory originally conceived by William Irvine. The heart of Irvinism was Irvine's doctrine of heat capacity, which stated that the total amount of caloric contained in a body was a simple product of its heat capacity and its absolute temperature (counted from absolute zero, signifying a complete absence of heat).

  Isothermal phenomena. Phenomena that take place at a fixed temperature. For example, the production of steam from water under constant pressure is assumed to be an isothermal process; a gas that expands or contracts isothermally obeys Boyle's law.

  Iteration. See epistemic iteration.

  Joule's conjecture. As designated by William Thomson, the idea from James Joule that all of the mechanical work spent in the adiabatic compression of a gas is converted into heat. Julius Robert Mayer advanced a similar but broader idea, which came to be known as Mayer's hypothesis, of which there are many possible formulations (see Hutchison 1976a).

  Joule-Thomson experiment. A series of experiments first performed by James Joule and William Thomson in the 1850s, also known as the porous plug experiment. Joule and Thomson pushed various gases through either a narrow opening or a porous plug and observed the resulting changes in their temperature. The amounts of temperature change were interpreted as indications of the extent to which the actual gases deviated from the ideal gas; hence, the results of the Joule-Thomson experiment were also used to calculate corrections of gas thermometer readings in order to obtain values of absolute temperature.

  Kinetic theory of gases. The popular theory of gases fully developed in the second half of the nineteenth century, in which the gas molecules are understood to be in random motion interrupted by frequent collisions with the walls of containers and with each other. In the kinetic theory, temperature is interpreted to be proportional to the average kinetic energy of the molecules.

  Laplacian physics. As characterized by the historian of science Robert Fox (1974), the tradition of physics spearheaded by Pierre-Simon Laplace. It was a "Newtonian" corpuscular tradition, in which various phenomena were understood as resulting from unmediated forces acting between pointlike particles of matter. Laplace reinterpreted the action of caloric in this manner, too.

  Latent heat. Heat that is absorbed into a body without raising its temperature, for example, when a solid melts and a liquid boils. Latent heat phenomena were most notably observed by Joseph Black. In the chemical caloric theory, latent heat was understood as combined caloric. In Irvinist caloric theory, latent heat phenomena were attributed to changes in the heat capacities of bodies.

  Material theory of heat. Any theory of heat, including any variety of the caloric theory, that regards heat as a material substance (cf. dynamic theory of heat).

  Mayer's hypothesis. See Joule's conjecture.

  Mechanical theory of heat. See dynamic theory of heat.

  Melting point. The temperature at which a solid melts. In the context of thermometry, an unspecified "melting point" usually refers to the melting point of ice. Although the melting point of ice is commonly considered to be the same as the freezing point of water, there have been doubts on that question.

  *Method of mixtures. A calorimetric method of testing the correctness of thermometers, practiced most effectively by Jean-André De Luc. Measured-out portions of water at two previously known temperatures are mixed, and the calculated temperature of the mixture is compared with the reading given by a thermometer under test. By this method De Luc argued for the superiority of mercury to all other thermometric liquids.

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  Metrology. The science or art of making measurements.

  *Metrological extension. A type of operational extension in which the measurement method for a concept is extended into a new domain.

  *Metrological meaning. The meaning of a concept that is given by the methods of its measurement (cf. operational meaning).

  Mixtures. See method of mixtures.

  Nomic measurement. See problem of nomic measurement.

  One-point method. Any method of graduating thermometers using only one fixed point (cf. two-point method). With this method, temperature is measured by noting the volume of the thermometric fluid in relation to its volume at the one fixed-point temperature.

  *Ontological principle. Ontological principles are those assumptions that are commonly regarded as essential features of reality within an epistemic community, which form the basis of intelligibility. The justification of an ontological principle is neither by logic nor by experience.

  *Operational extension. An aspect of the semantic extension of a concept, which consists of the creation of operational meaning in a domain where it was previously lacking.

  *Operational meaning. The meaning of a concept that is embodied in the physical operations whose description involves the concept. It is broader than metrological meaning, although it has often been used to designate metrological meaning by many commentators including Percy Bridgman.

  Operationalism, or operationism. The philosophical view that the meaning of a conce
pt is to be found primarily or even solely in the methods of its measurement. It has often been attributed to Percy Bridgman, though Bridgman himself denied that he had meant to propose a systematic philosophy while he continued to advocate operational analysis as a method of clarifying one's thinking.