# Popular Science Monthly/Volume 5/May 1874/Sketch of James P. Joule, F.R.S.

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JAMES PRESCOTT JOULE
* SKETCH OF DR. JAMES P. JOULE, F. R. S.
IF the discovery of chemical analysis by means of the spectrum be accepted as the most brilliant scientific achievement of the present century, the research by which the conservation of energy became established on a basis of exact quantitative experiment must be regarded as far more profound and important in its consequences. This great generalization, beyond doubt, is the property of no single intellect. Many men, in different countries, had independently arrived at the conception, and had furnished various kinds and degrees of evidence that it was true, but the honor of its first experimental demonstration, by which the quantitative convertibility of forces may be established, belongs to the subject of the following sketch.
James Prescott Joule was born at Salford, England, on Christmas-eve, 1818, and was privately educated at home. He early showed a taste for scientific study, and, at the age of fifteen, became a pupil of Dr. John Dalton, the chemist. This celebrated man—atomist and Quaker—came to Manchester, and became Professor of Mathematics and Natural Philosophy in the New College; and, when that was removed to York, he remained as a private teacher of the same subjects. By him, young Joule was initiated into mathematics, and trained in the art of experiment.
Mr. Joule's attention was early turned in a direction which naturally led him to his great discovery. At an early age he took up the ​subject of electro-magnetic engines; the idea of using electricity as a motive power being then a favorite one among scientific men. He made inventions to employ electro-magnetic force as a motor, and his first scientific paper was upon this subject. But the result of his investigations was the abandonment of any expectation of obtaining a valuable power from electro-magnetism. But, while giving up the hope of arriving at any important economical conclusions, Mr. Joule continued his researches on the laws which govern the lifting and sustaining power of the electro-magnet. Early in 1841 he gave, in the form of a lecture in the Royal Victoria Gallery, Manchester, the result of his experiments on a new class of magnetic forces, with the preliminary statement of what had been done by M. Jacobi, of St. Petersburg, and himself, in the way of applying magnetism as a motive power. Mr. Jacobi, it may be remarked, is reputed to have been the first who constructed an electro-magnetic machine capable of producing continuous movement, and which was for a long time used in impelling a boat on the Neva. Mr. Joule subsequently continued this investigation in conjunction with Dr. Scoresby, and from the results of their calculations it appeared that a grain of coal consumed by a steam-engine will raise 143 pounds one foot high, while a grain of zinc consumed in a voltaic battery can raise theoretically only 80 pounds. The cost of power by electro-magnetism was estimated to be twenty-five times greater than the cost of an equal amount of steam-power. Mr. Joule had arrived at the theory of the magnetic engine when twenty-one years of age, and in 1840 he had published a paper in Sturgeon's "Annals of Electricity," demonstrating that there is "no variation in economy, whatever the arrangement of the conducting metal, or whatever the size of the battery." Kindred to the subject of electro-motive machines is that of the air-engine, to which Mr. Joule gave considerable attention.
"Dr. Joule has pursued several lines of inquiry conjointly with other philosophers. His communication to the Royal Society, 'On the Changes of Temperature produced by the Rarefaction and Condensation of Air,' in which he pointed out the dynamical cause of the principal phenomena, and described the experiments on which his conclusions were founded, led Prof. Thomson, of Glasgow, to embark with Dr. Joule in a series of elaborate investigations 'On the Thermal Effects of Fluids in Motion.' The first of their series of four papers was read before the Royal Society, in June, 1853; the last in June, 1862. The whole will be found published at length in the 'Philosophical ​Transactions.' Dr. Lyon Playfair and Dr. Joule have also published an account of a conjoint investigation into the volumes occupied by bodies, both in the solid form and when dissolved in water, and have obtained results of an unexpected nature as well as of great value. Among other curious results, they found that 'many salts, when dissolved in water, do not add to the bulk of the water more than is due to the water actually present in the salts.' They have further shown that 'when salts do add to the bulk of the water in which they are dissolved, the increase of the bulk corresponds to that of a volume, or some multiple of a volume of water.'"
Dr. Joule's inventive talent was early shown in the construction of galvanometers. In 1863 he described to the Manchester Society his new and extremely sensitive thermometer, which was able to detect the heat radiated by the moon. When the moonbeam passed gradually across the instrument, the index was deflected several degrees, first to the right and then to the left; thus showing that the air in the instrument had been heated a few ten-thousandths of a degree by the influence of the rays. These experiments were lately referred to by the present Earl Rosse in a lecture on the same subject delivered at the Royal Institution.
It was about 1840 that Dr. Joule began to direct his special attention to the subject of heat. He made a communication to the Royal Society in that year, announcing the discovery of a principle in the development of heat by the voltaic principle, in which he established relations between heat and chemical affinity. This paper is recognized as containing the germ of the subsequent unfoldings of dynamical science in relation to chemical action.
The old view of the nature of heat still prevailed, although the declarations of Bacon and Locke, and the researches of Rumford and Davy, had undermined the notion that heat was a subtile matter or material agent diffused throughout all bodies, and had prepared the way for its apprehension as a mode of molecular motion. The first noteworthy advance toward the establishment of the mechanical theory of heat was made by Séguin, a Frenchman, in 1839, and by Mayer, a German, in 1842, who had propounded the hypothesis that the heat evolved in compressing an elastic fluid is exactly equivalent to the compressing force. But the theory was not yet established upon an experimental basis, so as to command the assent of the scientific world.
Independently of what had been done by others, and working in his own line, Dr. Joule had established relations, as we have seen, between heat and chemical affinity in 1840, and, some two years later, he applied the dynamical theory to steam-engines, to electro-magnetic engines, to vital processes, and to chemistry. "His paper on the 'Electric Origin of Heat' was a first communication, in 1842, to the meeting of the British Association at Manchester––the last meeting, ​by-the-way, at which Dalton appeared; and, on August 21, 1843, a circumstance which requires special mention, he communicated a second paper to the Association, then meeting at Cork, in which he describes a series of experiments on magneto-electricity, executed with a view to determine the mechanical value of heat. Experiments, with a like object, on the condensation of air, were communicated to the Association in 1844; and in 1845 his important paper, 'On the Mechanical Equivalent of Heat,' detailed the results he had gained from water agitated by a paddle-wheel. In following years, the same subject was perseveringly prosecuted, by numerous and yet more accurate experiments, until his grand determination was finally reached. In an elaborate paper, read before the Royal Society, January 21, 1849, and published in the 'Philosophical Transactions' of 1850, we have the results thus stated: 1. 'The quantity of heat produced by the friction of bodies, whether solid or liquid, is always proportional to the quantity of force expended;' 2. 'The quantity of heat capable of increasing the temperature of a pound of water by 1° Fahr., requires for its evolution the expenditure of a mechanical force required by the fall of 772 pounds through the space of one foot.' "
Dr. Tyndall gives the following explanation of the term "footpounds," used as a measure by Joule: "The quantity of heat which would raise one pound of water one degree in temperature is exactly equal to what would be generated if a pound-weight, after having fallen 772 feet, had its moving force destroyed by collision with the earth. Conversely, the amount of heat necessary to raise a pound of water one degree would, if applied mechanically, be competent to raise a pound-weight 772 feet high, or it would raise 772 pounds one foot high. The term 'foot-pound' expresses the lifting of one pound to the height of a foot. Thus the heat required to raise the temperature of one pound of water one degree being taken as a standard, 772 foot-pounds constitute what is called the mechanical equivalent of heat."
A sharp controversy arose a few years since in England as to the relative merits of Mayer and Joule in contributing to the establishment of the truth of the mechanical equivalent of heat. Dr. Joule states his own relation to the investigation as follows: "Mayer," he says, "appears to have published his views for the express purpose of securing priority. He did not wait until he had the opportunity of supporting them by facts. My course, on the contrary, was to publish only such theories as I had established by experiments calculated to commend them to the scientific public, being well convinced of the truth of Sir John Herschel's remark, that 'hasty generalization is the bane of science.' . . . I therefore fearlessly assert," writes Dr. Joule, in August, 1862, "my right to the position which has been generally accorded to me by my fellow-physicists, as having been the first to give decisive proof of the correctness of this theory."
​Prof. Tyndall, although the English champion of Mayer's claims, did ample justice to his own countryman, as the following passage shows: "It is to Mr. Joule, of Manchester, that we are almost wholly indebted for the experimental treatment of this subject. With his mind firmly fixed on a principle, and undismayed by the coolness with which his first labors appear to have been received, he persisted for years in his attempts to prove the invariability of the relation between heat and ordinary mechanical force. He placed water in a suitable vessel, agitated it by paddles moved by measurable forces, and determined the elevation of temperature; he did the same with mercury and sperm-oil. He caused disks of cast-iron to rotate against each other, and measured the heat produced by their friction. He urged water through capillary tubes, and measured the heat thus generated. The results of his experiments leave no doubt upon the mind that, under all circumstances, the absolute amount of heat produced by a definite amount of mechanical force is fixed and invariable."
For this great scientific achievement the Royal Medal of the Royal Society was awarded to Mr. Joule in 1852; and eight years later, when men of science began more fully to apprehend the great value of the discovery, he was presented also with the Copley Medal of the Royal Society. On that occasion, Sir Edward Sabine, the president, alluding to the former award, used the following words: "Both awards refer to the same experiments, and are substantially for the same great step in natural philosophy. You are all aware that a great principle has been added to the sum of human knowledge—one fruitful in consequences in a thousand ways, and which, being accepted among undisputed truths, is now embodied, without question, alike in the most wide-ranging speculations and the most matter-of-fact practice. The award of two medals for the same researches is an exceedingly rare proceeding in our society, and rightly so. The council have, on this occasion, desired to mark by it, in the most emphatic matter, their sense of the special and original character and high desert of Mr. Joule's discovery. No words of mine could add to the value of the award."
Dr. Joule has figured but little in the fields of popular science, having only given a few lectures to the people in Manchester, and published no book, as we are aware, of any kind. But his contributions to scientific periodicals and the transactions of learned societies are very numerous, and give the results of prolonged and incessant original investigations, extending through many years. He became a Fellow of the Royal Society in 1850, received the degree of B. C. L. from Oxford, of LL. D. from the Universities both of Dublin and of Edinburgh, is a corresponding member of the Institute of France, and was President-elect of the British Association for the Advancement of Science, which met at Bradford last year.