History of heat
The history of heat has a prominent place in the history of science. It traces its origins to the first hominids to make fire and to speculate on its operation and meaning to modern day physicists who study the microscopic nature of heat. The phenomenon of heat and its definition through mythological theories of fire, to heat, to Terra pinguis, phlogiston, to fire air, to caloric, to the theory of heat, to the mechanical equivalent of heat, to Thermos-dynamics (sometimes called energetics) to thermodynamics. The history of heat is a precursor for developments and theories in the history of thermodynamics.
The ancients viewed heat as that related to fire. The ancient Egyptians in 3000 BC viewed heat as related to origin mythologies. One example, is the theory of the Ogdoad, or the “primordial forces”, from which all was formed. These were the elements of chaos, numbered in eight, that existed before the creation of the sun.
The first to have put forward a semblance of a theory on heat was the Greek philosopher Heraclitus who lived around 500 BC in the city of Ephesus in Ionia, Asia Minor. He became famous as the "flux and fire" philosopher for his proverbial utterance: "All things are flowing." Heraclitus argued that the three principal elements in nature were fire, earth, and water. Of these three, however, fire is assigned as the central element controlling and modifying the other two. The universe was postulated to be in a continuous state of flux or permanent condition of change as a result of transformations of fire. Heraclitus summarized his philosophy as: "All things are an exchange for fire."
As early as 460 BC Hippocrates, the father of medicine, postulated that:
Heat, a quantity which functions to animate, derives from an internal fire located in the left ventricle.
In the 11th century AD, Abū Rayhān Bīrūnī cites movement and friction as causes of heat, which in turn produces the element of fire, and a lack of movement as the cause of cold near the geographical poles:
The earth and the water form one globe, surrounded on all sides by air. Then, since much of the air is in contact with the sphere of the moon, it becomes heated in consequence of the movement and friction of the parts in contact. Thus there is produced fire, which surrounds the air, less in amount in the proximity of the poles owing to the slackening of the movement there.
a) that [natural heat] would be the heat of a fiery atom that is broken, and b) that heat may occur through motion-change, the proof of this being through experiment.
In 1253, a Latin text entitled Speculum Tripartitum stated:
Avicenna says in his book of heaven and earth, that heat is generated from motion in external things.
Around 1600, the English philosopher and scientist Francis Bacon surmised that:
Heat itself, its essence and quiddity is motion and nothing else.
This echoed the mid-17th-century view of English scientist Robert Hooke, who stated:
Heat being nothing else but a brisk and vehement agitation of the parts of a body.
In 1761, Scottish chemist Joseph Black discovered that ice absorbs heat without changing temperature when melting. From this he concluded that the heat must have combined with the ice particles and become latent. Between 1759 and 1763 he formulated a theory of latent heat on which his scientific fame chiefly rests, and also showed that different substances have different specific heats. James Watt, who later invented the Watt engine, was Black's pupil and assistant.
The ability to use heat transfer to perform work allowed the invention and development of the steam engine by inventors such as Thomas Newcomen and James Watt. In addition, in 1797 a cannon manufacturer Sir Benjamin Thompson, Count Rumford demonstrated through the use of friction that it was possible to convert work to heat. He designed a specially shaped cannon barrel, thoroughly insulated against heat loss, then replaced the sharp boring tool with a dull drill bit, and immersed the front part of the gun in a tank of water. To the amazement of observers, he brought cold water to a boil within two and one half hours, without the use of fire.
Several theories on the nature of heat were developed. In the 17th century, Johann Becher proposed that heat was associated with an undetectable material called phlogiston which was driven out of a substance when it was burnt. This was finally refuted by Lavoisier demonstrating the importance of oxygen in burning in 1783. He proposed instead the caloric theory which saw heat as a type of weightless, invisible fluid that moved when out of equilibrium. This theory was used in 1824 by the French engineer Sadi Carnot when he published Reflections on the Motive Power of Fire. He set forth the importance of heat transfer: "production of motive power is due not to an actual consumption of caloric, but to its transportation from a warm body to a cold body, i.e. to its re-establishment of equilibrium." According to Carnot, this principle applies to any machine set in motion by heat.
Another theory was the kinetic theory of gases, the basis of which was laid out in 1738 by the Swiss physician and mathematician Daniel Bernoulli in his Hydrodynamica. In this work, Bernoulli first proposed that gases consist of great numbers of molecules moving in all directions, that their impact on a surface causes the gas pressure. The internal energy of a substance is the sum of the kinetic energy associated with each molecule, and heat transfer occurs from regions with energetic molecules, and so high internal energy, to those with less energetic molecules, and so lower internal energy.
The work of Joule and Mayer demonstrated that heat and work were equivalent forms of energy, and led to the statement of the principle of the conservation of energy by Hermann von Helmholtz in 1847. Clausius demonstrated in 1850 that caloric theory could be reconciled with kinetic theory provided that the conservation of energy was employed rather than the movement of a substance, and stated the First Law of Thermodynamics.
Heat is not a substance, but a dynamical form of mechanical effect.
Heat in modern terms, is generally defined as a type of energy transferred due to a temperature difference or that generated by friction.
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