Physilicious

Most physics texts are written as if they were supplementary problem books for math courses. They are heavy on the problem-solving, but light (or empty) on the cause-effect relationships, inductive thinking, and reasoning which makes science.

David Harriman is one physicist and teacher who has remedied that. He has a physics course for sale, which is described by the VanDamme Academy, where he teaches, as follows:

David Harriman, philosopher and historian of physics, is the originator of VanDamme Academy's revolutionary science curriculum. An expert both in physics and in proper pedagogy, Mr Harriman developed and taught a two-year course on the history of physics for VanDamme Academy. His unique approach is to teach physics historically, thereby teaching it inductively. From the early Greeks to Copernicus to Newton, this course presents the essential principles of physics in logical sequence, placing each in the context of the earlier discoveries that made it possible and explaining how each was discovered by reasoning from observations.

Teaching physics by this method not only renders physics thoroughly intelligible--it also makes physics an inspiring story of discovery, in which great thinkers triumph in their quest to grasp the nature of the physical universe.

He sells the CD for $495 and the DVD for $695.

He is not the first to teach physics from a historical perspective. Two others are Dr. Michael Fowler and Dr. Herbert Priestley. While Fowler and Priestley probably did not have the philosophic knowledge (e.g., of induction, deduction, and epistemology in general) of Harriman, they did have a knowledge of physics and its history. And they have some things available for less cost for those of us who cannot yet afford Harriman's work.

The homepage of Dr. Michael Fowler, at UVa, has links to his lectures for

PHYS 109: Galileo and Einstein (Lecturer) Fall

PHYS 152: Introductory Physics for Majors (Lecturer) Spring

PHYS 609: Galileo and Einstein (Lecturer) Fall

PHYS 751: Quantum Theory I (Lecturer) Fall

PHYS 752: Quantum Mechanics II (Lecturer) Spring

His also has notes available for Physics 252: Modern Physics.

On another page you can find: (1) a lecture on using history to teach physics; (2) a leture on heat which teaches physics from a historical (and hence inductive) perspective; (3) a lecture on electricity and magnetism which also teaches from a historical perspective; (4) a lecture on the development of Maxwell’s equations; (5) some quizzes, exercises, and another lecture.

Dr. Herbert Priestley wrote a book entitled Introductory Physics. You can find it on a used-book site such as Alibris or Abe Books.

Introductory Physics by Herbert Priestley (Allyn and Bacon, Inc., 1958) has the best presentation of physics I’ve ever seen. (I have not heard Harriman yet.) He presents concepts in their historical and scientific context. Priestley presents alternative viewpoints that were being used to understand phenomena such as heat or electricity, discusses why each viewpoint was held and the arguments scientists had, and describes the experiments the scientists did – especially the experiments which validated one side or the other. In showing us the development of ideas in physics, Priestley is showing us the correct view of concept-formation and the formation of generalizations, Priestley is showing us that true concepts and propositions come from applying rational, objective methods to the real world.

Priestley attended the University of Leeds, receiving a B.S. in 1933 and a Ph.D. in physics in 1935. He served in the Royal Air Force as an industrial research physicist, civilian education officer, and air intelligence officer. He came to the US as RAF liaison officer in 1942, but stayed on to teach physics at Ripton College after WWII. In 1952, he became chairman of the physics department at Knox College, where he stayed until he retired in 1980. His obituary is on Knox College Website.

A caveat. Priestley does not give Aristotle proper credit as a scientist. People have insulted Aristotle for centuries, for things that are not Aristotle’s fault – people throughout history blindly believed what was written in Aristotle’s corpus, yes, but that is not Aristotle’s fault. Aristotle, in method, was objective, and referred to experience. If he had the evidence available to him which people did who lived 1,000 years or more after he lived, he could have arrived at the conclusions we have -- even Galileo said this. He was a solid scientist in his context, as can be seen in the work he did most: philosophy, logic and biology.

Dr. James Lennox, Professor of Philosophy and the History of Science at the University of Pittsburgh, has some well-written and well-researched articles on his website regarding Aristotle as scientist and philosopher of science. An article directly relevant to some of Priestley's uninformed, unresearched accusations against Aristotle is Lennox's "Aristotle, Galileo and the Mixed Sciences," which discusses (1) Aristotle's use of mathematics as a tool in physics to explain why things happen and (2) Galileo's debt to Aristotle.

Dr. Michael Fowler, Professor of Physics at the University of Virginia also recognized Aristotle’s solid contributions to science. In a lecture on Aristotle, Dr. Fowler says:

To summarize: Aristotle's philosophy laid out an approach to the investigation of all natural phenomena, to determine form by detailed, systematic work, and thus arrive at final causes. His logical method of argument gave a framework for putting knowledge together, and deducing new results. He created what amounted to a fully-fledged professional scientific enterprise, on a scale comparable to a modern university science department. It must be admitted that some of his work - unfortunately, some of the physics - was not up to his usual high standards. He evidently found falling stones a lot less interesting than living creatures. Yet the sheer scale of his enterprise, unmatched in antiquity and for centuries to come, gave an authority to all his writings.

And on the website of the University of Dayton’s History Department, in an article about the history of science, they say:

Aristotle is the key figure in this history of ancient science and indeed one of a handful of leading thinkers and doers in the entire history of science from the dawn of man to the present. His work in virtually every scientific field--from biology to physics to chemistry to astronomy--became a cornerstone of Western Science until the Scientific Revolution. And indeed his methodology, his reliance upon close observation and interdisciplinary bent, remain with us today.

Here are some excerpts from Priestley’s book. It is impossible to grasp Priestley’s masterful and rational approach in brief excerpts, so the excerpts must be lengthy. Priestley does use math in his textbook (it is algebra-based), but these excerpts will focus on his discussions of cause and effect and the development of ideas.

I. Excerpt 1: Chp. 15, “Electricity and Chemistry,” pp. 201-205

15.1 Galvanism. Electricity and chemistry are closely inter-related. A chemical reaction can produce a supply of electricity for as long as the reaction continues. This, the first source of a continuous supply of electricity, an electric current, is the principle of the electric battery. Conversely, an electric current can produce a chemical reaction, usually the decomposition of a chemical compound into its simpler elements, the process of electrolysis. Both processes involve the conversion of energy from one form to another; in the first case, chemical energy becomes electrical energy; in the other, the reverse takes place.

Every living cell produces electricity. The functioning of living tissue today is studied through its electrical action. The study of electricity in living tissue, which began quite accidentally about one hundred and fifty years ago, led to the development of the electric battery, for many years thereafter the standard method of producing electricity

About 1750, it was noted that pieces of lead and silver placed above and below the tongue, respectively, with their outer edges in contact, produced an unpleasant and pungent taste not encountered when the metals were placed separately upon the tongue. The phenomenon was attributed to some excitation of the nerves of the tongue. By this time, various physicians and experimenters had demonstrated that electricity could be used as a muscular stimulant in man and animals. This fact had been used to distinguish between paralyzed and atrophied muscles, an electric charge producing a contraction only in a paralyzed muscle.

Before the end of the eighteenth century it was known that an electric discharge passed through the body of a freshly killed animal could cause a convulsive action in its muscles, and that the discharge of an electric eel (section 14.2) produced motion in a nearby dead fish. Identification of the origin of these effects was made by Galvani (1737-1798), a professor of anatomy at Bologna. Galvani began experimenting about 1780, using a Leyden jar [A Leyden jar was the earliest form of electric condenser, consisting of “a bottle filled with water into which was inserted a wire held in place by a cork.” p. 191] and an electrostatic machine to test the effects of the electric discharge upon the nervous system of the frog. During these experiments he made the chance observation that nearby electrical discharge caused convulsions in a freshly prepared frog’s leg in conducting contact with the earth.

[I] had dissected and prepared a frog. [While] attending to something else, I laid it on a table on which stood an electrical machine at some distance…when one of the persons present touched accidentally and lightly the inner [thigh or leg] nerves of the frog with the point of a scalpel all the muscles of the legs seemed to contract again and again as if affected by powerful cramps. [One of my assistants] thought…the action was excited when a spark was discharged from the conductor of the machine [and] called my attention to it…I was eager to test the same and to bring to light what was concealed in it. I therefore myself touched one of the other nerves with the point of the knife and at the same time one of those present drew a spark. The phenomenon was always the same. Without fail there occurred lively contractions in every muscle of the leg at the same instant as that in which the spark jumped…

[Thinking] these motions might arise from the contact with the point of the knife…rather than by the spark, I touched the same nerves again in the same way in other frogs with the point of the knife…with greater pressure [while] no one during this time drew off a spark...no motion could be detected. I [concluded] that perhaps to excite the phenomenon…needed both the contact of a body and the electric spark.

Therefore, I again pressed the blade of the knife on the nerve and kept it there at rest while the spark passed and while the machine was not in motion. The phenomenon only occurred while the sparks were passing. [In many experiments with the same knife] it was remarkable that when the spark passed the motions observed sometimes occurred and sometimes not… The scalpel had a bone handle...if this handle was held in the hand no contractions occurred when the spark passed; but they did occur if the finger rested on the metallic blade or on the iron rivet by which the blade was held in the handle…

Now to put the thing beyond all doubt we…not only touched the nerves of the leg [with a slender dry and clean glass rod] but rubbed them hard while the sparks were passing. But…the phenomenon never appeared. [It] occurred however if we even lightly touched the same nerve with an iron rod and only little sparks passed. [William F. Magie, A Source Book in Physics (New York: McGraw-Hill Book Company, Inc., 1938), p. 421.]

Galvani’s “phenomenon” occurred only when the frog’s leg was in conducting communication with the earth, first by chance contact of the scalpel with the nerve, thereafter intentionally by bringing the leg into contact with a conductor grounded by contact with the human body. He continued his researches, turning to the effect of atmospheric electricity (lightning) on muscular motion. He attached frogs by the nerves to long iron wires, the feet of the frogs being grounded by similar wires. Simultaneously with a flash of lightning the muscles were markedly convulsed.

In both these series of experiments the frog, place upon a body insulated from the ground, became charged by induction (section 14.11) from either the electrostatic machine or lightning. When a grounded metal object (scalpel or iron rod) touched the nerve, the sudden change of potential caused by grounding produced the observed convulsive action.

[I next laid one of the prepared frogs] on an iron plate and began to press the hook which was in the spinal cord against the plate. Behold, the same contractions, the same motions…other metals [gave] the same result, only that the contractions were different [for] different metals…more lively for some and more sluggish for the others. At last it occurred to us to use other [non-conducting] bodies…[dry] glass, rubber, resin, stone or wood. With these...no muscular contractions and motions could be seen. Naturally [this astonished us] and caused us to think that possibly the electricity was present in the animal itself…a very fine nervous fluid which during the occurrence of the phenomenon flows from the nerves to the muscle like the electric current….” [ibid., p. 424.]

Galvani now recognized that here was something entirely new. “to make the thing plainer” he varied the experiment by placing the frog on a glass non-conducting plate. A curved rod connected the hook which entered the spinal cord with the muscles of the leg or feet. Convulsions occurred only when the curved rod was of conducting material and only when the hook and conducting rod were of dissimilar metals.

Two possible explanations of these phenomena suggested themselves to Galvani; that there was electricity in the animal organism, or that there was involved some electrical process depending upon contact of the metals and for which the frog’s legs merely served as a sensitive detector. He leaned toward the first of these – the existence of “animal electricity,” for which the nerves had the greatest affinity and were the repository. His theory further assumed that the inner substance of the nerve served as the conductor of this electricity, while the outer layer of the nerve prevented its dispersal. The muscles were the receivers of the animal electricity, and were charged negatively on the outside and positively on the inside. The mechanism of motion was a discharge of the electric fluid from the inside to the outside of the muscle by way of the nerve (like the discharge of a Leyden jar), and this discharge provided a muscular contractional stimulus to the muscle fibers.

15.2 Volta disagrees with Galvani. Galvani’s experiments and his interpretation of the results aroused considerable interest. Among the physicists, physiologists, and medical men who obtained frogs and pieces of dissimilar metals to repeat the experiments for themselves was Volta (1745-1827), a countryman of Galvani’s and professor of physics at Paris.

Volta, greatly impressed by Galvani’s work, referred to it as “one of those splendid major discoveries which…serve to usher in new epochs, not only because it is new and wonderful but also because it opens up a broad field of experiments that are especially and outstandingly capable of the application. “ [ibid., p. 443.] Volta’s original belief in the correctness of the “animal electricity” theory was weakened when he found that a muscular contraction could be produced simply by allowing a very weak electrical discharge to traverse a nerve without the discharge in anyway passing through the muscles. To produce a contraction required only stimulation of “the nerves that control the motions of the voluntary muscles concerned.”

A physicist rather than a physiologist, Volta now shifted his emphasis to the function of the metallic rods used. Repeating the experiment of placing on the tongue two dissimilar metals, he “covered the point of the tongue...with a strip of tin…With the bowl of a spoon, I touched the tongue further back; then I inclined the handle of the spoon to touch the tin. I expected…a twitching of the tongue…. The expected sensation, however, I did not perceive at all; but instead, a rather strong acid taste at the tip of the tongue…this taste lasts as long as the tin and sliver are in contact with each other. …This shows that the flow of electricity from one place to another is continuing without interruption.” It was “not less remarkable” that reversing the experiment so that the silver touched the tip of the tongue and the tin its middle gave “a very different taste...no longer sour but more alkaline, sharp, and approaching bitter.” [ibid., p. 444.] Bringing together the free ends of strips of dissimilar metal which touched, respectively, the forehead and palate produced, at the instant of contact, a bring flash clearly visible to the eye.

Investigations such as these gradually convinced Volta that the metals not only served as conductors but actually generated the electricity themselves. He accordingly modified his views to the belief that the nerves were merely stimulated by a cause to be found in the metals themselves, which were “in a real sense the exciters of electricity.” By 1794 he declared his opposition to the idea of animal electricity and substituted the term “metallic electricity.” The entire effect arose from the electricity set into circulation when metals were brought into contact with any moist body. This circulation through nerves caused stimulation of associate muscles. He found that the results depended upon the nature of the substances used and drew up a series of substances (metals, graphite, an charcoal) such that the magnitude of the effect produced using any two of the substances increased with the separation of the substances in this series.

Volta now dispensed entirely with the use of nerves and muscles in his investigations, and brought pairs of metals into contact with various moist substances, such as paper, cloth, etc. With a sensitive electrometer which he had previously developed, he was able to show the existence of “contact potential” – that the momentary contact of two dissimilar metals caused them to become oppositely charged, even without any moist substance present. A zinc and a copper disc after being placed in contact were both found to be charged, the zinc positively and the copper negatively. Copper also became negatively charged after contact with iron or tin, although less strongly than after contact with zinc. On the other hand, contact with gold or silver gave copper a positive charge and the gold or silver a negative charge. By numerous experiments along these lines, Volta constructed a series for the metals such that upon bringing any two of them into contact, the earlier in the list became positively charged, the later one negatively charged:

Zinc copper
Lead silver
Tin gold
Iron graphite

Furthermore, the more widely separated the substances in the series, the greater was the contact charge developed between them.

On the basis of his investigations, Volta originally assumed that the exciting electricity was located only at the points of contact of the metals and that the animal or other fluid served only as a conductor. But further experiments showed that an electric charge can be produced not only between metals in contact, but also between a metal and certain fluids. For instance, an insulated disc of silver or other metal brought into contact with moist wood or paper and then removed was found to be negatively charged. Experimenting further with liquids and metals, Volta found that the best results were obtained from two dissimilar metals with a moist conductor between them, a combination called a galvanic element. The effect of such a single element was multiplied by combining a large number of them to form a “pile.”

In 1800, Volta described a pile which produced a constant flow of electricity. By comparison with a Leyden jar, it was “equal only to a [Leyden jar] very feebly charged; but infinitely surpasses the power of these [jars] in that it does not need, as they do, to be charged in advance by means of an outside source; and in that It can give the disturbance every time that it is properly touched no matter how often.” [ibid., p. 428]

The pile consisted of small, clean and dry discs of zinc and silver and discs of a spongy material capable of absorbing and retaining a liquid. On a table or base is placed a sliver plate, then a

plate of zinc; on this…one of the moistened discs; then another silver [plate], followed immediately by another of zinc, [then another] moistened disc…continue in the same way coupling a plate of sliver with one of zinc, always [in the same order] and inserting between these couples a moistened disc. [ibid.]

Such a pile produced a slight shock when the hands were placed in contact with the top and bottom of the pile, and also the previously experienced effect upon the nerves of taste, sight, and hearing. One drawback was that the moist material between the metal discs dried out, decreasing the electric current generated. To overcome this, Volta devised his “crown of cups,” consisting of a row of beakers of non-metallic material filled with brine into which were placed alternate strips of sliver and zinc. Each silver strip in one cup was joined to the zinc strip in the next cup by a metallic jumper. “A train of 30, 40, 60 of these goblets joined up in this manner…in substance is the same as the [pile] tried before; the essential feature, of the immediate connection of the different metals which form each pair and the mediate connection of one couple with another by the intermediary of a damp conductor, appears in this apparatus as well as in the other.” [ibid., p. 431.] This crown of cups was subsequently improved by substituting copper for silver and dilute sulphuric acid for brine.

Volta reported that the “tension” (potential difference) produced by the pile or cups “is less according as they are nearer in the following series…sliver, copper, iron, tin, lead, zinc, a scale in which the first [is positive with respect] to the second, the second to the third, etc.”

The importance of Volta’s discovery of a means of producing a continuous supply of electricity cannot be overemphasized. Sarton, the distinguished historian of science, compares it with the development of the telescope and microscope, with the fundamental difference that the telescope and microscope “were only means of magnifying our vision. They enabled us to see things which we could not see before, but which existed nevertheless… On the contrary, the electric cell was really a creative instrument; it opened to man a new and incomparable source of energy.” [Bern Dibner, Galvani-Volta (Norwalk: Burndy Library, Inc., 1952), p. 40.]

15.3 The simple voltaic cell. Volta’s identification of the true origin of “animal electricity” led to the familiar batteries now used in radios, automobiles, etc. In every case, production of electricity results from the conversion of chemical into electrical energy. To understand the mechanism involved, consider the simple or voltaic cell, consisting of two dissimilar metals immersed in a liquid, and in essence an element of Volta’s pile.

Genius. Thank you Dr. Priestley.

Priestley then goes on to discuss the work of Michael Faraday in discovering the laws of electrolysis, which led to the development of practical cells, i.e., the batteries we now have in everyday life, and which we take for granted.

But what we have in this excerpt is the scientific history of the development of the modern battery – which came out of experiments which changed fundamentally how we view man, as well. The observation that we had different sensations when metals touched our tongue in different places would have gone nowhere and could have been interpreted in all kinds of ways, without the knowledge that frogs’ nerves and muscles are affected by electricity.

This knowledge was the first step in our modern science of neurology, in understanding how the brain works, and in developing some of the drugs we have today (which have neurological effects because of their chemistry and electrical effects).

And if not for the foundational work of Michael Faraday arising from the research of Volta and Galvani, we would not know what we do today about nutrition and the operation of the cell. What does something so everyday as Gatorade have in it? Electrolytes. Thank Michael Faraday next time you drink some.

Priestley is a genius in taking us from the observation that we had certain sensations when metals touched our tongues, to the modern battery. He presents a missing side of modern scientific texts: causality. Science is about discovering cause-effect relationships. Most modern texts present physics as an exercise in mathematics – the texts could be addenda to math texts, providing word problems and applications of math. They fail miserably in presenting cause-effect relationships, and showing how scientific knowledge really develops. They fail to present the important experiments that led to modern understanding of the material world, and that make physics what it is.

II. Excerpt 2: Chp. 10, “The Nature of Heat,” pp. 135-139

10.6 The measurement of heat. The development of the thermometer opened the doorway to a new science – that of heat measurements – in which the pioneer was Joseph Black (1727-1799), professor of medicine and chemistry at the Universities of Glasgow and Edinburgh. Prior to Black’s work, no clear distinction had been drawn between “quantity of heat” and “degree of hotness (temperature).” While something clearly passed from a hot body to one at a lower temperature, whether that something was heat or temperature was not known. Black was the first to conceive clearly of heat as a measurably physical quantity, distinct from, although related to, temperature as indicated by a thermometer.

He began to investigate the general belief that the amount of heat required to raise the temperature of any body by a given amount was proportional to the density of the body. Fahrenheit, by mixing together water and mercury at different temperatures, had found that despite its much greater density, the heating and cooling effect of a given volume of mercury was only two-thirds that of the same volume of water. From these results Black concluded that “the quantities of heat which different kinds of matter must receive to reduce them to equilibrium with one another, or to raise their temperatures by an equal number of degrees, are not in proportion to the quantity of matter in each, by in proportions widely different from this.” [Abraham Wolf, A History of Science, Technology, and Philosophy in the 18th Century (New York: The Macmillan Company, 1939), p. 178.] Fahrenheit’s experiments led Back to compare the heating and cooling effects of other substances with corresponding effects of an equal bulk of water, obtaining for the different substances values he called their “capacities for heat.”
…
He went on to observe that the sensation of cold in a hand applied to a piece of ice indicates that the ice receives heat very rapidly. But a thermometer applied to the water dripping from the melting ice show it to be at the same temperature as the ice. “A great quantity, therefore, of the heat…which enters into the melting ice produces no other effect but to give it fluidity, without augmenting its sensible heat; it appears to be absorbed and concealed within the water, so as not to be discoverable by the application of a thermometer.” [ibid, p. 180.] Back now demonstrated that during the melting of ice, and similar changes of state (solid to liquid, liquid to vapor), large quantities of heat were “rendered latent,” absorbed with no change in temperature, and explained these and similar facts by assuming a union of the matter of heat with ice to form water and with water to form steam; i.e.,

Ice + matter of heat = water,
Water+ matter of heat = steam.

10.7 The caloric theory of heat. The more obvious phenomena of heat – combustion, melting, freezing, evaporation, etc. – have been familiar from early times, and ideas concerning the nature of heat go far back in history. Aristotle conceived of fire as one of the four material elements (section 4.2), while the Platonic view was that heat was some kind of motion: “For heat and fire…are themselves begotten by impact and friction: but this is motion.” But throughout the centuries little or no distinction was made between heat and flame.

Various people, including Francis Bacon, Huygens, and Boyle, advanced the idea that heat is a form of motion of the “parts” of a body. Boyle drew attention to the heat generated during the boring of guns and to the fact that “when a smith does hastily hammer a nail,…the hammered metal will grow exceedingly hot, and yet there appears not anything to make it so, save the forcible motion of the hammer.” [ibid, p. 276.] But there was no direct experimental support of these speculations.

Following his work on thermal capacities and latent heats, Black was led to consider the nature of heat. This he did with some reservations, as may be seen from the following extract from his lectures: “Heat is plainly something extraneous to matter. …Having arrived at this conclusion, it may perhaps be required of me to express more distinctly this something – to give a full description, or definition, of what I mean by the word ‘heat’ in matter. This, however, is a demand that I cannot satisfy entirely…. Our knowledge of heat is not brought to that state of perfection that might enable us to propose with confidence a theory of heat of to assign an immediate cause for it.” [Duane Roller, The Early Development of the Concepts of Temperature and Heat, (Cambridge; Harvard University Press, 1950), p. 42.]

Black continued with a review of the theories previously advanced as to the nature of heat, theories which fall into two basic categories – that heat is either motion or a material substance. Reviewing the motion theory, Black say that he “cannot form a conception of this internal (vibration) which has any tendency to explain even the more simple effects of heat.” He then goes on to point out that:

…the greater number of French and German philosophers have held that the motion of which they suppose heat to consist is not a tremor, or vibration, of the particles of the hot body itself, but of the particles of a subtle, highly elastic, and penetrating fluid matter, which is contained in the pores of hot bodies, or interposed among their particles…. But interposed among their particles…. But neither of these suppositions has been fully and accurately considered by their authors, or applied to explain the whole of the facts and phenomena relating to heat. They have not, therefore, supplied us with a proper theory or explication of the nature of heat.

A more ingenious attempt has lately been…given by the late Dr. Cleghorn…. He supposed that heat depends on the abundance of that subtle elastic fluid which had been imagined before by other philosophers to be present in every part of the universe and to be the cause of heat…. he supposed that the ordinary kinds of matter consist of particles having strong [gravitational] attraction both for one another and for the matter of heat; whereas the…matter of heat is self-repelling, its particles having a strong repulsion for one another while they are attracted by other kids of matter.

Such an idea of the nature of heat is the most probable of any that I know.… It is, however, altogether a supposition. [ibid., p. 45.]

In 1779, Cleghorn extended the material theory of heat to include Black’s discoveries of thermal capacity and latent heat. The main properties assigned by Cleghorn to the “matter of heat’ or “caloric,” may be summarized in the following postulates of the caloric theory:

1. Caloric is an elastic fluid, composed of particles which strongly repel each other.
2. Particles of caloric are attracted by particles of ordinary matter.
3. Caloric can be neither destroyed nor created.
4. Caloric can be either sensible caloric, which increases the temperature of body to which it is added and forms an “atmosphere” around the particles of the body, or latent caloric, which is combed with the particles of the body in a manner similar to the chemical combinations of the particles themselves, producing as a new compound the liquid or vapor form of the substance.
5. Caloric may or may not have appreciable weight.

When two bodies at different temperatures were placed in contact, it was supposed that caloric flowed from the hotter to the colder body until equilibrium was established. Expansion was attributed to the mutual repulsion of the caloric which entered the heated body. Development of heat by friction or compression was explained as due either to the fact that the particles of a body rubbed by friction lost some of their “capacity” for caloric, which was thus “liberated,” raising the temperature of the body, or to the fact that friction and pressure squeezed out some of the caloric latent in the pressed body, which thereby became sensibly hot. The caloric theory dominated the science of heat until the middle of the nineteenth century.

It should be noted that toward the end of the eighteenth century the “motion theory” of heat was nothing more than pure speculation, a working hypothesis without any decisive experimental evidence in its favor. By contrast the caloric theory offered a satisfactory and semiquantitative explantion of the known thermal phenomena. Furthermore, the motion theory dealt only with the origin of heat and said nothing about its behavior.

10.8 Does heat have weight? Black pointed out that the fact that bodies expanded when heated had led to the supposition that a heated body increased in weight. Various eighteenth-century experiments to test this supposition had produced conflicting results, none of them proving “that the weight of bodies is increased by their being heated, or by the presence of heat in them.” Some observers found that an increase in the temperature of a body was accompanied by slight increase in weight; some observed a slight loss in weight; others could detect no variation in weight with variation in temperature. The most carefully executed experiments were those of Runford, whose results were negative.

Although Rumford was an able administrator, and an authority on military problems, experimenting on heat was one of his “most agreeable employments.” He believed the mode-of-motion theory to be the sounder view of the nature of heat, even though in his time the caloric theory was well established and generally accepted. The primary purpose of his experiments was to attack the caloric theory from as many different points of view as possible.

Identical glass flasks containing equal weights of water, alcohol, and mercury showed equal temperatures and weights after having been exposed to room temperature (61º F) for 24 hours, after 48 hours at a cooler temperature (30º F), and upon being restored to room temperature after the cooler period. Repeated several times, the experiment gave consistent results. Rumford was convinced that “if heat be, in fact, a substance or matter…it must be something so infinitely rare, even in its most condensed state, as to baffle all our attempts to discover its [weight]… I think we may very safely conclude that all attempts to discover any effect of heat upon the apparent weights of bodies will be fruitless.” [Wolf, op. cit., p. 196.]

Rumford’s experiments showed heat had no detectable weight. So caloric must be imponderable, an opinion which Black had considered to be one of the chief objections to the caloric theory. But to many eighteenth-century scientists and philosophers this was not a serious objection. At that time full acceptance was given to a small class of “imponderable” fluids – including light, electricity, and magnetism – which, unlike ordinary matter, were not subject to gravitational attraction to any observable extent. By attributing to these “imponderables” certain other familiar properties of ordinary matter, the various known phenomena could be fairly satisfactorily explained, and new phenomena often successfully predicted Thus the problem of the weight of heat was not critical in resolving the conflict between the caloric and motion theories of heat. Much more critical was the conservation principle, that caloric could be neither created nor destroyed. Here also Rumford performed certain vital experiments as part of his general attack on the caloric theory.

The caloric theory had been particularly useful in explaining and predicting phenomena in mixing liquids or heating a substance over a fire, in which it is reasonable to conclude that there is no creation or destruction of heat during its conduction from object to object or from fire to object. But where did the heat come from when an object was warmed by rubbing it or hammering it? While the calorists believed they could answer this question and still retain the principle of conservation of caloric, other investigators believed the mode-of-motion theory to be a much more satisfactory explanation.

While engaged in boring cannon at Munich, Rumford observed with surprise “the very considerable degree of heat that a brass gun acquires in a short time in being bored, and with the still higher temperature of the metallic chips separated from it by the borer. The more I meditated on these phenomena, the more they appeared to me to be curious and interesting. A thorough investigation of them seemed even to bid fair to give a farther insight into the hidden nature of heat; and to enable us to form some reasonable conjectures respecting the existence, or nonexistence, of [caloric]….From whence comes the heat actually produced in the mechanical operations? Is it furnished by the metallic chips which are separated by the borer from the solid mass of metal?” [Roller, op. cit., p. 63.] In one experiment, for example, a 113-lb metal blank was heated from 60º F to 130º F while less than two ounces of metallic dust was produced by the borer.

A brass cylinder, placed in a wooden box containing 18 ¾ lbs of water, was made to rotate against a steel borer. The amount of heat produced could be determined by observing the rise in temperature of the water, which was brought from 60 F to the boiling point (212 F) in 2 ¾ hours. As Rumford stated: “It would be difficult to describe the surprise and astonishment expressed in the countenance of the by-standers on seeing so large a quantity of water heated, and actually made to boil without any fire…. We must not forget to consider that most remarkable circumstance, that the source of the heat generated by friction in these experiments, appeared evidently to be inexhaustible….anything which any insulated body, or system of bodies, can continue to furnish without limitation, cannot possibly be a material substance. It appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything capable of being excited and communicated in the manner in which the heat was excited and communicated in these experiments, except it be motion. “ [Wolf, op. cit., p. 197.]

Here Rumford emphasizes what he considers the chief result of his experiments, the apparently inexhaustible source of heat generated by friction. The calorists claimed heat is rubbed out of an object by friction. Ultimately, then, all the heat in the object should be exhausted. But this was never observed. Furthermore, in Rumford’s experiments heat apparently was created by friction, refuting the conservation principle which is the foundation of the caloric theory, and denying the material nature of heat, the basis of that conservation principle.

Rumford published the results of his experiments in 1798. One year later Humphrey Davy (1778-1829) published an essay directed against the caloric theory and which dealt in part with the production of heat by friction. The best-known of Davy’s experiments is that in which he rubbed together two blocks of ice fastened by wires to two bars of iron.

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Some forty years after the experiments of Rumford and Davy, the problem of heat produced by friction was again investigated, this time on a quantitative basis, by Mayer (in Germany) and Joule (in England). By 1850 these investigators had established beyond little doubt that heat is not a separate substance, but is a form of energy, the kinetic energy of the atoms and molecules of ordinary matter.

Again: genius. The interplay between theory, observation, reasoning and experiment is masterfully presented by Priestley.

Priestley goes on to discuss the work of J.B. Mayer and James Joule in determining the relationship between mechanical energy and heat and in discovering the principle of the conservation of energy.

Introductory Physics I highly recommend to anyone who wants a conceptual, rational understanding of the physical world we live in.