Popular Science Monthly/Volume 15/July 1879/Julius Robert Mayer

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Popular Science Monthly Volume 15 July 1879  (1879) 
Julius Robert Mayer
 
 
PSM V15 D302 Julius Robert Mayer.jpg
JULIUS ROBERT MAYER.

JULIUS ROBERT MAYER.

THE name of the remarkable man whose likeness we give in this number of the "Monthly" is now intimately and imperishably associated with the establishment of the most important scientific truth that has been developed during the last hundred years—the "Conservation of Energy." It is a truth belonging exclusively to no one man, and to no one nation, but to an epoch of scientific advancement that was made by the labors of many distinguished investigators working independently of each other in different countries. In such circumstances it is easy to fall into error in estimating the merits of alleged discoverers. In the first place, there may be very great differences in the positions of men as respects favorable opportunities of making their work known. There is besides less familiarity with what is going on in foreign countries than near by; and there is, moreover, the warping influence of national prejudice by which the claims of men are liable to be exaggerated at home and depreciated abroad. There is undoubtedly less of this bias in science than in any other sphere of intellectual exertion, but this sphere is by no means free from it. It was the fortune of Mayer to suffer from all these causes, and to such a degree that his character as an original discoverer has been denied on very high authority. The ground was strenuously maintained that he had no right whatever to a place among the founders of the great modern doctrine of the "Correlation of Forces." This denial led to investigation and sharp controversy, the result of which was not only to vindicate his claims to be ranked among the discoverers of the new principle, but it was shown that he was probably ahead of all others in grasping and developing it. Now that he has passed away, it is proper to review the subject, which may prove instructive as a chapter of scientific history, as well as interesting in its personal bearing. As we find the investigation thoroughly worked out and most admirably presented in the searching controversy which has now become memorable in the annals of discovery, we shall quote freely from the materials before us so as to present to our readers as faithfully as possible the considerations on the strength of which the claims of Mayer first became recognized.

As regards the life of Mayer the details are meager. He was born in Heilbronn, Würtemberg, November 25, 1814. He received his early education in the gymnasium of his native town, and studied medicine at Tübingen, finishing his course in Munich and Paris. In 1840 he made a voyage on a Dutch freighter to Java, and spent the summer of that year in professional practice at Batavia. Returning to Heilbronn he first became county wound-physician, and afterward physician to the city, and while giving the main portion of his time to professional labors he devoted himself systematically, and with great assiduity, to original scientific researches on the wide subject of the "Conservation of Forces." In the revolution of 1848 Dr. Mayer took what was called the side of order, which roused against him the antagonism of many of his neighbors. He believed that he had made very important discoveries which were unrecognized and were ascribed to others, while his scientific works were attacked and discredited in a way that preyed upon his feelings and disturbed his mind. This was aggravated by the loss of his children, and he fell into an excited and sleepless condition. Being suddenly seized with a fit of delirium on May 28, 1850, he quitted his bed and leaped from a second-story window, thirty feet high, to the street below. He recovered from the shock, but his mind was so seriously affected that he was sent to a lunatic asylum. Dr. Mülburger, physician to the institution, states that the equilibrium of his mental and emotional nature was seriously affected, one of the symptoms being that, "if you conversed with him about a scientific topic, it was very hard to keep him to the point: his ideas were profound, it is true, surprisingly so, but they came disconnected; they went to the heart of the subject, but they did not hold on to it. He was subject to occasional fits of uncontrollable rage, and on feeling them coming on he would ask to be put in one of the strong cells of the asylum. These fits came on only three or four times during the four months he spent at the asylum, and they did not last long. He had a very strong thirst for spirituous liquors, an inclination which was the result of his mental malady, and the gratification of which increased it." He was at length restored to health, and busied himself with grape culture at Heilbronn. He died in his native town on March 20, 1878, aged sixty-three years.

The following lucid account of Mayer's labors and judicial estimate of his position were made by Professor Tyndall in 1871, and are so admirable that we quote them in full, in preference to anything that it would be possible for us to write:

Dr. Julius Robert Mayer was educated for the medical profession. In the summer of 1840, as he himself informs us, he was at Java, and there observed that the venous blood of-some of his patients had a singularly bright red color. The observation riveted his attention; he reasoned upon it, and came to the conclusion that the brightness of the color was due to the fact that a less amount of oxidation sufficed to keep up the temperature of the body in a hot climate than in a cold one. The darkness of the venous blood he regarded as the visible sign of the energy of the oxidation.

It would be trivial to remark that accidents such as this, appealing to minds prepared for them, have often led to great discoveries. Mayer's attention was thereby drawn to the whole question of animal heat. Lavoisier had ascribed this heat to the oxidation of the food. "One great principle," says Mayer, "of the physiological theory of combustion is, that under all circumstances the same amount of fuel yields, by its perfect combustion, the same amount of heat; that this law holds good even for vital processes; and that hence the living body, notwithstanding all its enigmas and wonders, is incompetent to generate heat out of nothing."

But beyond the power of generating internal heat, the animal organism can also generate heat outside of itself. A blacksmith, for example, by hammering can heat a nail, and a savage by friction can warm wood to its point of ignition. Now, unless we give up the physiological axiom that the living body can not create heat out of nothing, "we are driven," says Mayer, "to the conclusion that it is the total heat generated within and without that is to be regarded as the true calorific effect of the matter oxidized in the body."

From this, again, he inferred that the heat generated externally must stand in a fixed relation to the work expended in its production. For, supposing the organic processes to remain the same, if it were possible, by the mere alteration of the apparatus, to generate different amounts of heat by the same amount of work, it would follow that the oxidation of the same amount of material would sometimes yield a less, sometimes a greater, quantity of heat. "Hence," says Mayer, "that a fixed relation subsists between heat and work, is a postulate of the physiological theory of combustion."

This is the simple and natural account, given subsequently by Mayer himself, of the course of thought started by his observation in Java. But the conviction once formed, that an unalterable relation subsists between work and heat, it was inevitable that Mayer should seek to express it numerically. It was also inevitable that a mind like his, having raised itself to clearness on this important point, should push forward to consider the relationship of natural forces generally. At the beginning of 1842 his work had made considerable progress; but he had become physician to the town of Heilbronn, and the duties of his profession limited the time which he could devote to purely scientific inquiry. He thought it wise, therefore, to secure himself against accident, and in the spring of 1842 wrote to Liebig, asking him to publish in his "Annalen" a brief preliminary notice of the work then accomplished. Liebig did so, and Dr. Mayer's first paper is contained in the May number of the "Annalen" for 1842.

Mayer had reached his conclusions by reflecting on the complex processes of the living body; but his first step in public was to state definitely the physical principles on which his physiological deductions were to rest. He begins, therefore, with the forces of inorganic nature. He finds in the universe two systems of causes which are not mutually convertible: the different kinds of matter and the different forms of force. The first quality of both he affirms to be indestructibility. A force can not become nothing, nor can it arise from nothing. Forces are convertible, but not destructible. In the terminology of his time, he then gives clear expression to the ideas of potential and dynamic energy, illustrating his point by a weight resting upon the earth, suspended at a height-above the earth, and actually falling to the earth. He next fixes his attention on cases where motion is apparently destroyed, without producing other motion; on the shock of inelastic bodies, for example. Under what form does the vanished motion maintain itself? "Experiment alone," says Mayer, "can help us here." He warms water by stirring it; he refers to the force expended in overcoming friction. Motion in both cases disappears; but heat is generated, and the quantity generated is the equivalent of the motion destroyed. "Our locomotives," he observes with extraordinary sagacity, "may be compared to distilling apparatus: the heat beneath the boiler passes into the motion of the train, and is again deposited as heat in the axles and wheels."

A numerical solution of the relation between heat and work was what Mayer aimed at, and toward the end of his first paper he makes the attempt. It was known that a definite amount of air, in rising one degree in temperature, can take up two different amounts of heat. If its volume be kept constant, it takes up one amount; if its pressure be kept constant, it takes up a different amount. These two amounts are called the specific heat under constant volume and under constant pressure. The ratio of the first to the second is as 1: 1·421. No man, to my knowledge, prior to Dr. Mayer, penetrated the significance of these two numbers. He first saw that the excess 0·421 was not, as then universally supposed, heat actually lodged in the gas, but heat which had been actually consumed by the gas in expanding against pressure. The amount of work here performed was accurately known, the amount of heat consumed was also accurately known, and from these data Mayer determined the mechanical equivalent of heat. Even in this first paper he is able to direct attention to the enormous discrepancy between the theoretic power of the fuel consumed in steam-engines and their useful effect.

Though this paper contains but the germ of his further labors, I think it may be safely assumed that, as regards the mechanical theory of heat, this obscure Heilbronn physician, in the year 1842, was in advance of all the scientific men of the time.

Having, by the publication of this paper, secured himself against what he calls "Eventualitäten," he devoted every hour of his spare time to his studies, and in 1845 published a memoir which far transcends his first one in weight and fullness, and indeed marks an epoch in the history of science. The title of Mayer's first paper was, "Remarks on the Forces of Inorganic Nature."[1] The title of his second great essay was, "Organic Motion in its Connection with Nutrition." In it he expands and illustrates the physical principles laid down in his first brief paper. He goes fully through the calculation of the mechanical equivalent of heat. He calculates the performances of steam-engines, and finds that 100 pounds of coal, in a good working engine, produce only the same amount of heat as 95 pounds in an unworking one; the 5 missing pounds having been converted into work. He determines the useful effect of gunpowder, and finds nine per cent, of the force of the consumed charcoal invested on the moving ball. He records observations on the heat generated in water agitated by the pulping engine of a paper manufactory, and calculates the equivalent of that heat in horse-power. He compares chemical combination with mechanical combination—the union of atoms with the union of falling bodies with the earth. He calculates the velocity with which a body starting at an infinite distance would strike the earth's surface, and finds that the heat generated by its collision would raise an equal weight of water 17,356° C. in temperature. He then determines the thermal effect which would he produced by the earth itself falling into the sun. So that here, in 1845, we have the germ of that meteoric theory of the sun's heat which Mayer developed with such extraordinary ability three years afterward. He also points to the almost exclusive efficacy of the sun's heat in producing mechanical motions upon the earth, winding up with the profound remark that the heat developed by friction in the wheels of our wind-and water-mills comes from the sun in the form of vibratory motion; while the heat produced by mills driven by tidal action is generated at the expense of the earth's axial rotation.

Having thus, with firm step, passed through the powers of inorganic nature, his next object is to bring his principles to bear upon the phenomena of vegetable and animal life. Wood and coal can burn; whence come their heat, and the work producible by that heat? From the immeasurable reservoir of the sun. Nature has proposed to herself the task of storing up the light which streams earthward from the sun, and of casting into a permanent form the most fugitive of all powers. To this end she has overspread the earth with organisms which, while living, take in the solar light, and by its consumption generate forces of another kind. These organisms are plants. The vegetable world, indeed, constitutes the instrument whereby the wave-motion of the sun is changed into the rigid form of chemical tension, and thus prepared for future use. With this prevision, as will subsequently be shown, the existence of the human race itself is inseparably connected. It is to be observed that Mayer's utterances are far from being anticipated by vague statements regarding the "stimulus" of light, or regarding coal as "bottled sunlight." He first saw the full meaning of De Saussure's observation as to the reducing power of the solar rays, and gave that observation its proper place in the doctrine of conservation. In the leaves of a tree, the carbon and oxygen of carbonic acid, and the hydrogen and oxygen of water, are forced asunder at the expense of the sun, and the amount of power thus sacrificed is accurately restored by the combustion of the tree. The heat and work potential in our coal strata are so much strength withdrawn from the sun of former ages. Mayer lays the axe to the root of the notions regarding "vital force" which were prevalent when he wrote. With the plain fact before us that in the absence of the solar rays plants can not perform the work of reduction, or generate chemical tensions, "it is," he contends, "incredible that these tensions should be caused by the mystic play of the vital force." Such an hypothesis would cut off all investigation; it would land us in a chaos of unbridled phantasy. "I count," he says, "therefore, upon your agreement with me when I state, as an axiomatic truth, that during vital processes the conversion only, and never the creation of matter or force, occurs."

Having cleared his way through the vegetable world, as he had previously done through inorganic nature, Mayer passes on to the other organic kingdom. The physical forces collected by plants become the property of animals. Animals consume vegetables, and cause them to reunite with the atmospheric oxygen. Animal heat is thus produced; and not only animal heat, but animal motion. There is no indistinctness about Mayer here; he grasps his subject in all its details, and reduces to figures the concomitants of muscular action. A bowler who imparts to an eight-pound ball a velocity of thirty feet, consumes in the act one-tenth of a grain of carbon. A man weighing 150 pounds, who lifts his own body to a height of eight feet, consumes in the act one grain of carbon. In climbing a mountain 10,000 feet high, the consumption of the same man would be two ounces, four drachms, fifty grains of carbon. Boussingault had determined experimentally the addition to be made to the food of horses when actively working, and Liebig had determined the addition to be made to the food of men. Employing the mechanical equivalent of heat, which he had previously calculated, Mayer proves the additional food to be amply sufficient to cover the increased oxidation.

But he does not content himself with showing, in a general way, that the human body burns according to definite laws, when it performs mechanical work. He seeks to determine the particular portion of the body consumed, and in doing so executes some noteworthy calculations. The muscles of a laborer 150 pounds in weight weigh 64 pounds; but, when perfectly desiccated, they fall to 15 pounds. Were the oxidation corresponding to that laborer's work exerted on the muscles alone, they would be utterly consumed in eighty days. The heart furnishes a still more striking example. Were the oxidation necessary to sustain the heart's action exerted upon its own tissue, it would be utterly consumed in eight days. And, if we confine our attention to the two ventricles, their action would be sufficient to consume the associated muscular tissue in three and a half days. Here, in his own words, emphasized in his own way, is Mayer's pregnant conclusion from these calculations: "The muscle is only the apparatus by means of which the conversion of the force is effected; but it is not the substance consumed in the production of the mechanical effect." He calls the blood "the oil of the lamp of life"; it is the slow-burning fluid whose chemical force, in the furnace of the capillaries, is sacrificed to produce animal motion. This was Mayer's conclusion twenty-six years ago. It was in complete opposition to the scientific conclusions of his time; but eminent investigators have since amply verified it.

Thus, in baldest outline, I have sought to give some notion of the first half of this marvelous essay. The second half is so exclusively physiological that I do not wish to meddle with it. I will only add the illustration employed by Mayer to explain the action of the nerves upon the muscles. As an engineer, by the motion of his finger in opening a valve or loosing a detent, can liberate an amount of mechanical motion almost infinite compared with its exciting cause, so the nerves, acting upon the muscles, can unlock an amount of activity wholly out of proportion to the work done by the nerves themselves.

As regards these questions of weightiest import to the science of physiology, Dr. Mayer, in 1845, was assuredly far in advance of all living men.

Mayer grasped the mechanical theory of heat with commanding power, illustrating it and applying it in the most diverse domains. He began, as we have seen, with physical principles; he determined the numerical relation between heat and work; he revealed the source of the energies of the vegetable world, and showed the relationship of the heat of our fires to solar heat. He followed the energies which were potential in the vegetable, up to their local exhaustion in the animal. But in 1845 a new thought was forced upon him by his calculations. He then, for the first time, drew attention to the astounding amount of heat generated by gravity where the force has sufficient distance to act through. He proved, as I have before stated, the heat of collision of a body falling from an infinite distance to the earth, to be sufficient to raise the temperature of a quantity of water, equal to the falling body in weight, 17,356° C. He also found, in 1845, that the gravitating force between the earth and sun was competent to generate an amount of heat equal to that obtainable from the combustion of six thousand times the weight of the earth of solid coal. With the quickness of genius he saw that we had here a power sufficient to produce the enormous temperature of the sun, and also to account for the primal molten condition of our own planet. Mayer shows the utter inadequacy of chemical forces, as we know them, to produce or maintain the solar temperature. He shows that were the sun a lump of coal it would he utterly consumed in five thousand years. He shows the difficulties attending the assumption that the sun is a cooling body; for, supposing it to possess even the high specific heat of water, its temperature would fall 15,000° in five thousand years. He finally concludes that the light and heat of the sun are maintained by the constant impact of meteoric matter. I never ventured an opinion as to the truth of this theory; that is a question which may still have to be fought out. But I refer to it as an illustration of the force of genius with which Mayer followed the mechanical theory of heat through all its applications. Whether the meteoric theory be a matter of fact or not, with him abides the honor of proving to demonstration that the light and heat of suns and stars may be originated and maintained by the collisions of cold planetary matter.

Let us now go back ten years and see how this verdict was arrived at.

When Professor Tyndall was preparing his work on heat, he desired to acquaint himself with all that Mayer had done upon this subject. He accordingly wrote to two eminent Germans, authorities upon this question, for information. Both responded, and one of them, Professor Clausius, procured Mayer's publications to send to Tyndall. In his first letter he said he thought Professor Tyndall would not find anything very important in Mayer's writings. But before forwarding the memoirs he read them himself, and then wrote to Tyndall: "I must here retract the statement, in my last letter, that you would not find much matter of importance in Mayer's writings; I am astonished at the multitude of beautiful and correct thoughts which they contain." He then went on to point out various important subjects in the treatment of which Mayer had anticipated other eminent writers. Professor Tyndall perfectly agreed with Clausius, and resolved to do his share toward making so able and original a man better known in England. Accordingly, on June 6, 1862, he gave a most interesting lecture at the Royal Institution, full of new views and novel experiments, on the subject of "Force." At its close he remarked: "To whom, then, are we indebted for the striking generalizations of this evening's discourse? All that I have laid before you is the work of a man of whom you have scarcely ever heard. All that I have brought before you has been taken from the labors of a German physician, named Mayer. Without external stimulus, and pursuing his profession as town physician in Heilbronn, this man was the first to raise the conception of the interaction of natural forces to clearness in his own mind. And yet he is scarcely ever heard of in scientific lectures, and even for scientific men his merits are but partially known. Led by his own beautiful researches, and quite independent of Mayer, Mr. Joule published his first paper on the 'Mechanical Value of Heat,' in 1843; but in 1842 Mayer had actually calculated the mechanical equivalent of heat from data which a man of rare originality alone could turn to account. From the velocity of sound in air, Mayer determined the mechanical equivalent of heat."

In October of the same year there appeared an article in " Good Words," under the title of " Energy," the joint production of Professors Thomson and Tait, which was called forth by Tyndall's June lecture on "Force." In this paper and in subsequent ones, defending it, the writers confess themselves startled at the recent attempt made "to place Mayer in a position which he never claimed," and they deny to him " the credit of being the first to establish in its generality the principle of the 'Conservation of Energy,' "and assert that " Mayer's paper (1842) has no claims to novelty or correctness at all, saving this, that by a lucky chance he got an approximation to a true result from an utterly false analogy"; and that " even on this point he had been anticipated by Séguin, who three years before the appearance of Mayer's paper had obtained and published the same numerical result from the same hypothesis. " They claim that the honors of producing this theory are English throughout; that Newton, Rumford, and Davy established it, and that Dr. Joule, of Manchester, developed and matured it; and, impelled by a proper "scientific patriotism," they protest against this attempt of Tyndall to make over to a foreigner what belongs to his own countrymen, and is withheld by depreciation and suppression.

These positions were met and the whole case of Professors Thomson and Tait exploded in a series of communications addressed by Professor Tyndall to the " Philosophical Magazine." As to the statement that Mayer himself did not claim to be a founder of the "Dynamical Theory of Heat," Professor Tyndall quoted the following passage from a publication of Mayer's in 1851: "The new subject " (the mechanical theory of heat) " soon began to excite the attention of learned men, but, inasmuch as both at home and abroad the subject has been exclusively treated as a foreign discovery, I find myself compelled to make the claims to which priority entitles me; for, although the few investigations which I have given to the public, and which have almost disappeared in the flood of communications which every day sends forth, without leaving a trace behind, prove by the very form of their publication that I am not one who hankers after effect, it is not therefore to be assumed that I am willing to be deprived of intellectual property which documentary evidence proves to be mine."

As to the declaration that Mayer's views of 1842 had no novelty or correctness at all, save what he luckily blundered into, Professor Tyndall first quotes some counter-authorities. In Professor Helmholtz's celebrated discourse, delivered at Königsberg, in 1854, on the interaction of natural forces, this great physicist remarks, " The first man who correctly perceived and rightly enunciated the general law of nature which we are here considering was a German physician, J. R. Mayer, of Heilbronn, in the year 1842." Again, M. Verdet, an eminent French authority, especially in the literature of science, in addressing the Chemical Society of Paris on the mechanical theory of heat in 1862, remarked: "I now come to the researches which, from 1842 to 1849, definitely founded the science. These researches are the exclusive work of three men[2] who, without concert and without knowing each other, arrived simultaneously in almost the same manner at the same ideas. The priority in the order of publication belongs, without any doubt, to the German physician, Jules Robert Mayer, whose name has occurred so often in these lectures; and it is interesting to know that it was by reflecting on certain observations in his medical practice that he perceived the necessity of an equivalence between work and heat. . . . He perceived in the act of respiration the origin of the motive power of animals; and the comparison of animals with thermic engines afterward suggested to him the important principle with which his name will be connected for ever. . . . We also find in the same memoir (1842) a first determination of the mechanical equivalent of heat deduced from the properties of gases, which is perfectly exact in principle."

How Dr. Mayer arrived at the mechanical equivalent of heat, has been briefly referred to by Tyndall in a previous quotation. It will not be possible here to go into the full detail of Mayer's method, but the reader who is curious about it may consult Tyndall's "Heat as a Mode of Motion" for a clear statement, and, for a still completer account, vol. xxviii. of the "Philosophical Magazine," Fourth Series, page 25. Before they had become familiar with Dr. Mayer's work, Professors Thomson and Tait had no word for him but that cf disparagement; but, as his results were forced upon their attention, they were compelled to concede something to him, and so Tait admits, in 1863, that "Mayer's later papers are extremely remarkable and excessively interesting, and certainly deserve high credit." Yet his claim as the first to determine the mechanical equivalent of heat is still pointedly denied. Indeed, Professor Tyndall himself does not lay the highest stress upon this achievement of Dr. Mayer. He observes: "I must here say distinctly that I would not for an instant allow my estimate of Mayer to depend upon his determination of the mechanical equivalent of heat. It is the insight which he had obtained in advance of all other men regarding the relationship of the general energies of the universe, as illustrated in the whole of his writings, that gives him his claim to my esteem and admiration."

Now, undoubtedly the whole is greater than a part, and Mayer's fame has a far broader foundation than any one special result could afford. But we think that his determination of the mechanical equivalent of heat, in the year 1842, with the resources he had, and the exactness which he attained, is one of the most marvelous exploits in the whole history of science, is incomparably his greatest achievement, and is sufficient alone to place him in advance of all the thinkers who have devoted themselves to this great research. And we apprehend that this would have long ago been conceded but for the rival claims of Dr. Joule to this discovery. It is admitted on all hands, and even by Mayer himself, that Joule's laboratory processes were necessary and invaluable in completing the work, and placing this truth upon its firm and experimental basis. With great patience and skill he worked out the law of the mechanical equivalence of heat, as a demonstration that all men can verify, and, by the award of the whole scientific world, that law is permanently connected with his name. But Joule's results were reached only in 1849, while Mayer had arrived at the same result by other methods in 1842. What was it that both men were driving at? It was the working out of a great relation, or the establishment of a universal truth of nature. . Mayer reached it, by using the data that science had created for him. He got it first, he got it independently, and he got it exactly, or within a small fraction of the expression arrived at by Joule after six years of subsequent experiment. Mayer was the pioneer, the revealer, the creator of the theory, and Joule the verifier of his work. That verification was required and has made the name of Joule immortal; but who will compare 'it with that master stroke of genius by which from scanty materials the great truth was first independently seized and formulated? In 1849 Dr. Joule fixed the exact mechanical equivalent of heat after many laborious experiments, at 772 foot-pounds. Seven years previously Dr. Mayer pursued a method which gave the mechanical equivalent of heat as 771·4 foot-pounds.

It was alleged by Thomson and Tait, as we have seen, that Mayer's method had been adopted by the Frenchman Séguin, three years earlier, and that he anticipated the German in deducing the mechanical equivalent of heat. Séguin, in 1839, published a work on the steam engine, in Paris; and that work contains a table on the relations of pressures, temperatures, and mechanical effects of steam, from which it was alleged that the mechanical equivalent of heat may be inferred. But the widest discrepancies existed among the interpretations of these tables by different authorities. Upon a careful investigation of the subject Professor Tyndall found that Séguin's and Mayer's numerical results did not refer to the same things at all, and that Séguin's tables did not attempt to give the mechanical equivalent of heat. Professor Tyndall says: "It is only necessary, however, to read the foregoing pages to see that Mayer and Séguin are speaking of two totally different things; that the degrees of the one are not the degrees of the other; that the 'temperatures correspondantes' of the latter, which refer to his compressed steam, are not thermal units at all, and that there is no determination whatever of the mechanical equivalent of heat in the above table."

We have no space to go further into the particulars of this controversy, which was as discreditable to the assailants of Mayer as it was honorable to his disinterested defender. It is to be remembered that on all occasions, and in the most emphatic way, Professor Tyndall bore his testimony to the greatness of Dr. Joule's work, and deprecated every construction of his efforts which assumed that he was exalting the German at the expense of the Englishman. His demand was that Dr. Mayer be accorded a distinguished place among the founders of the modern doctrine of forces—such a place as he was incontestably entitled to by the scope, originality, and earliness of his work. But his opponents would allow the German doctor no merit whatever as a pioneer or discoverer, and no place in the circle of eminent men who created the new epoch of dynamical philosophy. The attack, however, upon Mayer signally failed of its intended purpose, and the parties who made it had the mortification of seeing that their ungenerous exertions were overruled to an end very different from that which they had designed. After the sifting and probing which followed the onslaught of the Scotchmen, the claims in behalf of Mayer were universally recognized as just; he was chosen by acclamation a member of the French Academy of Sciences, and the award of the Copley medal in 1871, the highest honor in the gift of the Royal Society of England, was the sharp rebuke of British Science to the unworthy efforts incited by a spurious patriotism to depreciate an illustrious foreign savant.

Dr. Mayer, as we have intimated, was a man of much suffering, which was undoubtedly aggravated by the neglect and injustice with which his labors were treated; and, when generous recognition of his services was made, the good effect on his disordered mind was palpable. It was while he was in the asylum, under treatment, that the Copley medal with Tyndall's accompanying letter was put into his hands. Dr. Mülburger, the attending physician, remarked, " I can still see him as he entered my room, beaming with gladness, to exhibit to me this rare distinction."

A monument is to be erected to Mayer at Heilbronn, and the scientific men of different countries are adding their contributions to those of his townsmen for the purpose of its erection.

  1. Translations of this and other important papers of Mayer are contained in the volume on the "Correlation of Forces," published by D. Appleton & Co., New York.
  2. Mayer, Colding, and Joule.