Summary of the letters of exchange in the 1902-1904 "What is Entropy", centered at London, by American thermodynamicist Sidney Reeve. [1]

“Eighteen months previously to its opening there was published in Engineering (July 13, 1900) a letter upon 'The Nature of Entropy', from Mr. J. MacFarlane Gray to Mr. T. O'Connor Sloane, which is worthy of notice. But the bulk of the expression of opinion occurred within the three months from early December, 1902, to early March, 1903, during which time forty odd contributions to the topic appeared in the columns of four London engineering periodicals, all of them from the pens of prominent men.”

	De Volson Wood	Mr. Richmond

“The discussion which followed this brief communication was a beautiful example of the way in which a society whose members are fresh from practical life and forgetful of the accurate definitions of modern science, may hopelessly involve itself when questions concerning the nature of energy are sprung.

Mr. Richmond arose, and with the assistance of the blackboard explained at length a method, in common use among the engineers of Europe, for obtaining the adiabatical equation in such a case as that of Professor Wood's “engine in which the law of pressures and volumes of the working fluid are represented on a diagram of energy by a closed path,” in which it is desirable to express in heat units the difference in amount between the heat absorbed and the heat emitted. Mr. Richmond emphasized the fact that by this method “absolutely no calculation” was required. It could “all be mastered by anybody with about an hour’s careful thought.”

Mr. Kent wanted Mr. Richmond to indicate more plainly what were the abscissae in his diagrams upon the board; and he desired, furthermore, to know whether these abscissac represented “entropy for work.”

Mr. Richmond responded that he had tactfully omitted the word “entropy” from his explanation because “most people had a notion that entropy was some sort of a mystery.” He thereupon proceeded to elucidate the mystery. If we represent a quantity of heat by a rectangle, the absolute temperature being represented on one side, the other side will represent the “entropy.” “It's simply the name ‘entropy.’ One is temperature, the other is entropy. The thing itself is so much simpler than the name that there is no trouble in understanding that if a rectangle represents the heat, one side representing the heat, the other must represent the ratio.”

Mr. Kent declared himself abundantly satisfied with Mr. Richmond’s explanation, and hoped Mr. Richmond would write it all out in a little treatise to be printed in the Transactions—omitting the calculus.

Mr. Rockwood did not wish to appear frivolous, but thought Mr. Richmond would confer a favor on the world of steam engineers at large if he would inform the gentlemen present “Why he uses adiabatics, what adiabatics are for, and what they ever will be for.” “The prophetic eye,” he continued, “may discern what use they can subserve ; but at present it is perfectly plain that no gas ever expands adiabatically, or ever will, steam least of all, and the deductions arising from the analysis of adiabatic curves are wholly inapplicable to any known case of a gas or heat engine." Mr. Rockwood wanted to know what sort of a heat engine was going to be devised in the future to utilize all the mathematical theory evolved by distinguished writers in their investigation of the interesting adiabatic mystery.
Mr. Kent desired to ask whether this system was identical with that of Macfarlane Gray. Mr. Richmond responded that it was, and that its use being almost universal in Europe, he failed to understand why it had not been adopted in this country.

Mr. Kent knew why. It was because Mr. Richmond had not written the proposed treatise. “I heard Macfarlane Gray read his paper in 1889, and I do not think there were five men in the room that understood it. You were one of them, probably.”

Mr. Richmond, ignoring the Delphic ambiguity of Mr. Kent's last sentence, proceeded again to enlarge upon the extreme simplicity and unmathematical nature of his method.

Mr. Rockwood again incurred the risk of being deemed frivolous by asking Mr. Richmond to “dwell particularly upon the nature of heat and upon the nature of entropy, because therein he will do a great service for steam engineers.”

Mr. Kent expressed the hope that Mr. Richmond would not say anything in his treatise about the nature of heat. Quoting the dictum of Maxwell, “or somebody else” : “ What heat is we do not know,” he added impressively, “We do not know, and we are not going to know. There is no such thing as entropy.”

Mr. Rockwood insisted, nevertheless, that Mr. Richmond should be allowed to write his treatise.

Mr. Richmond declared Mr. Kent's sententious utterances to be, in the present case, a mathematical fiction. It was not a mathematical fiction, but an elementary concession, “the moment you allowed that energy is a quantity of two dimensions and you know one. When you represent that, the other dimensions, whether it has a name or not, is a clear factor.”

“As a young man I tried to read thermodynamics, but I always came up against entropy as a brick wall that stopped my further progress. If found the ordinary mathematical explanation, of course, but no sort of physical idea underlying it. No author seemed even to try to give any physical idea. Having in those days great respect for textbooks, I concluded that the physical meaning must be so obvious that it needs no explanation, and that I was especially stupid on the particular subject.”

“When Mr. Swinburne gravely informs an audience that two and three do not make five, but something else, everybody takes him to be joking, but when he tries to upset some other well-established scientific principles …he may be doing much harm [and] he does not know what he is talking about.”

A listing of mostly incorrect misinterpretations of entropy, in a letter to The Electrician (London) from Sydney Evershed, January 09, 1903, in connection to the great “what is entropy debate” (1902-1904) launched by British electrical engineer James Swinburne. [5]

(a) Entropy is that portion of the intrinsic energy of a system which cannot be converted into work by even a perfect heat engine (Clausius)
(b) Entropy is that portion of the intrinsic energy which can be converted into work by a perfect engine (Maxwell, following Tait).
(c) Entropy is that portion of the intrinsic energy which is not converted into work by our imperfect engines (Swinburne).
(d) Entropy, in a volume of gas, is that which remains constant when heat nether enters nor leaves the gas (R. Robinson).
(e) Entropy may be called the ‘thermal weight’, temperature being called the ‘thermal height’ (ibid).
(f) Entropy is one of the factors of heat, temperature being the other (Engineering).

“Astonishment [at seeing] a man so well known and so eminent in science as Sir Oliver Lodge putting forward ideas on thermodynamics which I have combated ever since the commencement of my studies in that science.”

“Swinburne has written one of the best and clearest expositions of the subject that has ever been written, especially when he points out that Nature never undertakes any change unless her interests are served by an increase in entropy.”

“I should like to ask Professor Max Planck whether the view he expresses that ‘Nature never undertakes any change unless her interests are served by an increase of entropy’ is to be taken with or without any particular reservation or with any special interpretation of ‘her interests’. My thermodynamic ideas are somewhat old-fashioned—viz., that there is invariably a dissipation of energy or loss of availability of energy due to imperfect or total want of reversibility in natural processes. This entirely agrees in effect with the way of expressing things in terms of increase of ‘entropy’, although that subtle quantity is certainly ‘ghostly’, and is somewhat too evasive to be regarded as a physical state even though it be a function of the physical state referred to a standard state. But the question is how the interests of Nature are served by imperfect reversibility? Professor Planck’s words suggest a choice on Nature’s part, as if Nature had any choice. Goethe said God himself could not alter the course of Nature. That was truly scientific. Then, again, what are to be considered the interests of Nature? Are we to take exactly things exactly as we find them, and define the interests in that way? If so, it carries us no further. Or is there a theorem of greatest entropy, showing how any variation from the proper course of Nature would tend to reduce the rate of increase of the entropy?”

“Whether entropy has any ‘ghostly’ attributes, is a question I will not open, but I am for the present quite content to know that it is a quantity which can be measured without ambiguity.”

“I do emphatically deny, and always have combated the proposition adduced by Mr. Heaviside, of the universal dissipation of energy.”