# Dictionary of National Biography, 1885-1900/Joule, James Prescott

​JOULE, JAMES PRESCOTT (1818–1889), physicist, son of Benjamin Joule of Salford (1784–1858) and his wife, Alice (1788–1836), the elder daughter of Thomas Prescott of Wigan, was born in New Bailey Street, Salford, on Christmas eve 1818. His ​father and grandfather, who came to Salford from Youlgreave in Derbyshire, were brewers, but the former disposed of the business in 1854, owing to failing health. As a boy Joule was delicate, and in consequence received his early education at home till he reached the age of sixteen. In 1835 he began with his brother Benjamin to study under Dalton, who was then president of the Manchester Literary and Philosophical Society. Dalton taught the boys algebra and geometry, and had just introduced them to chemistry when an attack of paralysis disabled him. But from this distinguished chemist Joule received his first inducement to undertake the work of an original scientific investigator. A room in his father's house was allotted to him as a laboratory, and he began electrical and magnetic experiments, which bore their first fruit in a published paper ‘On an Electro-magnetic Engine’ (Sturgeon, Annals of Electricity, 1838). Various other papers on magnetism and electro-magnetism followed; one of these, ‘On Electro-magnetic Forces’ (ib. 1840), describes almost the earliest attempt known to measure an electric current in terms of a unit. A unit current is defined by Joule as one which, if allowed to pass for an hour through a water voltameter, will decompose nine grains of water. In a lecture delivered at Manchester in February 1841 (ib. vol. viii.) Joule showed that the efficiency of the most nearly perfect electro-magnetic motor that he had contrived was, per lb. of zinc used in the battery, about one-fifth of the efficiency of a good Cornish pumping-engine per lb. of coal. ‘This comparison,’ he concluded, ‘is so very unfavourable that I confess I almost despair of the success of electromagnetic attractions as a means of power.’ The same lecture contains an account of his experimental discovery of the important fact, ‘suggested by an ingenious gentleman of this town,’ that an iron bar is increased in length on being magnetised. When Joule read his first paper—‘On the Electric Origin of the Heat of Combustion’—before the Manchester Literary and Philosophical Society (2 Nov. 1841), Dalton attended, and for the first time in his life moved a vote of thanks to the author. Joule was elected a member of the society 25 Jan. 1842, and was elected librarian in 1844, honorary secretary in 1846, a vice-president in 1851, and president for the first time in 1860. He regularly attended the society's meetings, and throughout his life found there his most congenial society.
In a paper ‘On the Production of Heat by Voltaic Electricity’ (Proc. R. S. 17 Dec. 1840) the first of the great laws with which Joule's name is imperishably connected was announced. The experiments are given in detail in the ‘Philosophical Magazine’ (xix. 260). Ohm in his work ‘Die galvanische Kette,’ 1827, had introduced and defined the accurate notions to which we now give the names of electro-motive force, current, and resistance, and had stated the law which goes by his name. Fairly satisfactory methods of comparing resistances had been devised, and Joule himself by his improvements had made the tangent galvanometer an accurate instrument for the measure of current. The fact that a current produced heat in a conductor through which it passed had been frequently observed, and Davy (Phil. Trans. 1821) had experimented on wires of different materials but of the same dimensions, arranging them in order according to the magnitude of the heat produced. Joule, however, in the paper now under consideration, was the first to announce the definite law that ‘when a current of voltaic electricity is propagated along a metallic conductor the heat evolved in a given time is proportional to the resistance of the conductor multiplied by the square of the electric intensity,’ i.e. electric current. In the same paper he showed that the law applies, when proper allowance is made for certain disturbances, to heat produced in electrolytes. The paper also contained the first reference to a ‘standard of resistance;’ this consisted of a coil of ten feet of copper wire .024 inch in thickness.
These experiments contained the germs of Joule's second great discovery, the equivalence of heat and energy, which he fully developed later. But he had already made it clear that the energy set free in the battery is also proportional to the resistance of the circuit and to the square of the current.
Joule embodied further results of his researches in important papers on the electro-motive forces of various forms of voltaic cells and the heats of combination of the materials of the cells. The results of his experiments down to 1843, and of the theoretical conclusions drawn from them, are summed up in a paper ‘On the Heat evolved during the Electrolysis of Water’ (Mem. Manchester Lit. and Phil. Soc. vol. vii.), and they still form an exposition of the leading principles of the energetics of the electric current. In reading these researches it must be remembered that the intensity of the current—in Ohm's words, its ‘Spannung’—is what we now call electro-motive force. The most important of his conclusions may be quoted: ‘Third—Hence it is that, however we arrange the voltaic apparatus, and whatever cells of electrolysis we include in the circuit, the whole ​caloric of the circuit is exactly accounted for by the whole of the chemical changes. Fourth—As was discovered by Faraday, the quantity of current electricity depends upon the number of atoms which suffer electrolysis in each cell, and the intensity depends upon the sum of the chemical affinities. Now both the mechanical and heating powers of a current are (per equivalent of electrolysis in any one of the battery cells) proportional to its intensity. Therefore the mechanical and heating powers of the current are proportional to each other. Fifth—The magnetic electrical machine enables us to convert mechanical power into heat by aid of the electric currents which are induced by it, and I have little doubt that by interposing an electro-magnetic engine in the circuit of a battery a diminution of the heat evolved per equivalent of chemical change would be the consequence, and that in proportion to the mechanical powers obtained.’ If in No 4 above we read electro-motive force for ‘intensity,’ it will be recognised as in accordance with our present knowledge of the subject.
The experimental question referred to in No. 5 was soon submitted to further test, and on 21 Aug. 1843 a paper, the first of a long series on the subject, ‘On the Calorific Effects of Magneto-Electricity and on the Mechanical Value of Heat,’ was read before the British Association at Cork (Phil. Mag. 3rd ser. vol. xxiii.; Collected Papers, i. 123). This remarkable paper describes a number of experiments in which a small electro-magnet was rotated in water in a magnetic field produced either by permanent magnets or by a fixed electro-magnet. The current induced in the moving coils, the total heat generated, and the energy used in maintaining the motion were all measured, and it was shown that the energy used and the heat produced were both proportional to the square of the current. Thus a constant ratio exists between the heat generated and the mechanical power used in its production, so that, to quote from the paper, ‘The quantity of heat capable of increasing the temperature of a pound of water by one degree of Fahrenheit's scale is equal to … a mechanical force capable of raising 838 pounds to a perpendicular height of one foot.’ A postscript to the same paper contains further important statements to the following effect: ‘I have lately proved experimentally that heat is evolved by the passage of water through narrow tubes. … I thus obtain one degree of heat per pound of water from a mechanical force capable of raising about 770 pounds to the height of one foot. I shall lose no time in repeating and extending these experiments, being satisfied that the grand agents of nature are by the Creator's fiat indestructible, and that wherever mechanical force is expended an exact equivalent of heat is always obtained.’ Thus in 1843, in his small laboratory at Pendlebury, near Manchester, Joule had determined by two distinct methods the physical constant now known as J., or ‘Joule's equivalent,’ and had shown conclusively that heat was a form of energy.
But further experiment was needed. The difference between 838 and 770 was too great to satisfy Joule's desire for exact knowledge. In a paper ‘On the Changes of Temperature produced by the Rarefaction and Condensation of Air’ (Phil. Mag. 3rd ser. May 1845; Collected Papers, i. 171) he described a determination of J. made by observing the heat produced by compressing air and the energy requisite for the compression; the result was 798 foot-pounds. In this paper he obtained the important result necessary to justify his procedure that ‘no change of temperature occurs when air is allowed to expand in such a way as not to develop mechanical power.’
The first series of observations on the development of heat by the friction of water, in which the now celebrated paddle-wheel was employed to stir the water, was communicated to the British Association at Cambridge in 1845. The number obtained was 890 foot-pounds.
A paper ‘On the Heat disengaged in Chemical Combinations’ (Phil. Mag. 4th ser. vol. iii.; Collected Papers, i. 205), though not published till 1852, belongs to the same period. It contains a description of one of the first, if not absolutely the first, really accurate galvanometers. The needle used was half an inch in length, while the coils were one foot in diameter. In 1846, in a paper ‘On the Effects of Magnetism upon the Dimensions of Iron and Steel Bars’ (Phil. Mag. 3rd ser. vol. xxx.; Collected Papers, i. 235), Joule returned to a subject he had discussed five years previously in Sturgeon's ‘Annals,’ and during the following year the fundamental principles of the doctrine of the conservation of energy were clearly stated by him in a popular lecture ‘On Matter, Living Force, and Heat’ (Manchester Courier, 5 and 12 May 1847; Collected Papers, i. 265).
In June 1844 Joule's father moved from Pendlebury to Whalley Range, where he built for his son a convenient laboratory near the house. In this, with the aid of the minutely accurate thermometers made under his direction in 1845 by Mr. Dancer, he was able to carry out more exact experiments on the value of J. as determined by the friction ​of water. These were communicated to the British Association at Oxford in June 1847. They led to the result 781.5. After the reading of this paper Joule and Sir William Thomson first met, and the acquaintance, to use Sir William's words, ‘quickly ripened into a life-long friendship.’
Joule's own account of this meeting, and of the general reception of his work at this time, is given in a note, dated 1885, to his ‘Collected Papers’ (ii. 215): ‘It was in 1843 that I read a paper “On the Calorific Effects of Magnetic Electricity and the Mechanical Value of Heat” to the chemical section of the British Association assembled at Cork. With the exception of some eminent men, among whom I recollect with pride Dr. Apjohn, the president of the section, the Earl of Rosse, Mr. Eaton Hodgkinson, and others, the subject did not excite much general attention, so that when I brought it forward again at the meeting in 1847, the chairman suggested that as the business of the section pressed I should not read any paper, but confine myself to a short verbal description of my experiments. This I endeavoured to do, and discussion not being invited, the communication would have passed without comment if a young man had not risen in the section, and by his intelligent observations created a lively interest in the new theory. The young man was William Thomson.’
Sir William Thomson says in a letter to Mr. Bottomley (Nature, 1882, xxvi. 619) that at first he thought Joule must be wrong, but as he listened he recognised that ‘Joule had certainly a great truth, and a great discovery, and a most important measurement to bring forward.’ He continues: ‘Joule's paper at the Oxford meeting made a great sensation. Faraday was there, and was much struck with it, but did not enter fully into the new views. It was many years after that before any of the scientific chiefs began to give their adhesion. It was not long after when Stokes told me he was inclined to be a Joulite.’
About a fortnight later Joule and Thomson met again by chance near Chamounix. Joule had just married, and was on his wedding tour, carrying a long thermometer, with which he was going to try for a rise of temperature in waterfalls, and the two arranged to make an experiment a few days later at the Cascade de Sallanches, but found it too much broken with spray. On his return to Manchester, encouraged, no doubt, by the reception of his work at Oxford, and aided by the generous enthusiasm of Thomson, Joule set himself to repeat his experiments on the production of heat by friction. The results were communicated to the Royal Society by Faraday on 21 June 1849, and printed during the following year in the paper ‘On the Mechanical Equivalent of Heat’ (Phil. Trans. 1850, pt. i.; Collected Papers, i. 298). The introduction to the paper contains a very fair account of the labours of others in the same field. A long series of observations, conducted with the utmost care, leads to the result that ‘the quantity of heat capable of increasing the temperature of a pound of water (weighed in vacuo, and taken at between 55° and 60° Fahr.) by 1° Fahr. requires for its evolution the expenditure of a mechanical force represented by the fall of 772 lb. through the space of one foot,’ or, in more modern phraseology, we should say, the expenditure of 772 foot-pounds of mechanical energy.
For nearly thirty years this result of Joule's stood alone as the one satisfactory determination of a most important physical constant. Writing in the ‘Proceedings’ of the American Academy for Arts and Sciences, 11 June 1879, Professor Rowland of Baltimore says: ‘We find that the only experimenter who has made the determination with anything like the accuracy demanded by modern science, and by a method capable of giving good results, is Joule, whose determination of thirty years ago, confirmed by some recent results to-day, stands almost, if not quite, alone among accurate results on the subject.’ Professor Rowland proceeds to explain the reasons why he undertook fresh experiments, and concludes that the difference between his own results and those of Joule is ‘not greater than 1 in 400, and is probably less.’
Researches on various subjects more or less cognate to the above continued to occupy Joule for some time longer. In 1840 Joule had himself established the connection between the work required to produce an electric current in a wire and the heat evolved. Sir William Thomson's papers on the dynamical theory of heat and various allied subjects were published in 1851 (Trans. R. S. E., 1851), and in a paper ‘On Applications of the Principle of Mechanical Effect to the Measurement of Electro-motive Forces and of Galvanic Resistances in Absolute Units’ (Phil. Mag. December 1851), he pointed out that Joule's measurements of 1840, combined with a knowledge of J., gave a means of measuring in absolute units the electrical resistance of the wire employed by him, or that conversely if the resistance of the wire were known absolutely the measurements could be used to determine J. The question of absolute electrical units was brought into ​prominence by Sir William Thomson, Clerk Maxwell, and others, at various meetings of the British Association; and in 1862, at the Cambridge meeting, the Committee of the Association on Standards of Electrical Resistance, appointed in the previous year, made their first report. In the next report (1863) Joule's name appears, and to him was entrusted the duty of determining the dynamical equivalent of heat from the thermal effects of electric currents. Before this could be done it was necessary to wait for the new standard of resistance, the ‘ohm.’ This was completed by Maxwell and Fleeming Jenkin in 1864, and in 1867 the committee reported that considerable progress in their work had been made, and that Joule's experiments on the heat generated in a voltaic current, the resistance of which was known in absolute measure, when conducted with every possible care, gave 783 as the value of the equivalent. The last experiments by friction had given the value 772, and Joule expressed himself as willing to make a new determination by the frictional method to determine if possible the cause of the discrepancy. An account of the electrical experiments is given in the British Association Report for 1867 (Report of the Committee on Electrical Standards, Appendix vi.)
The results of Joule's final experiments by the direct method of friction appeared in 1878 in a paper ‘On a New Determination of the Mechanical Equivalent of Heat’ (Phil. Trans. 1878, pt. ii.), and lead to the value 772.55, agreeing almost exactly with the value found in 1850. It appeared, therefore, that the cause of the discrepancy lay in the unit of resistance. Any doubt as to this was soon resolved, for Rowland, in the same year as Joule's last paper was published (American Journal of Science and Arts, 1878), showed that the standard of resistance was about 1 per cent. smaller than the committee of 1864 had intended it to be, and that, making this correction, the results of his own experiments by the methods of friction and of electrical heating agreed very closely both among themselves and also with Joule's value, 772.5. This result was confirmed in 1881 and 1882 by Lord Rayleigh, who found that the value of the British Association unit of resistance was .9867 instead of unity, while the value required to bring Joule's two determinations of J. into complete accordance is .9873. Thus the exactness of his work has been amply verified.
The full credit for establishing his great principle belongs to Joule; still others had been working more or less vaguely in the same field. Bacon, in the ‘Novum Organon,’ states his conviction that ‘the very essence of heat is motion and nothing else.’ Boyle, in his book ‘On Cold’ (1665), when discussing the primum frigidum, says: ‘For if a bodie's being cold signify no more than its not having its insensible parts so much agitated as those of our sensories, there will be no cause to bring in the primum frigidum … it suffices that the sun, or some other agent which agitated more vehemently its parts before, does now either cease to agitate them, or agitate them very remissly.’ But these and similar statements, such as that from Locke quoted by Joule in his paper of 1850, which may be found, are merely speculations.
The first experiments of value were those of Rumford about 1798, who produced by friction sufficient heat to raise 26.58 lb. of water from its freezing-point to its boiling-point, and concluded that heat was motion. In 1849 Joule himself called attention to these experiments, and showed that Rumford's numbers led to a value for the equivalent comparable with his own. Towards the end of the last century Sir Humphry Davy showed that ice could be melted by friction, even in a vacuum, when everything in the neighbourhood was at the freezing-point. Seguin in 1837 endeavoured to determine the equivalent from the loss of heat suffered by steam in expanding, and Mayer of Heilbronn in 1842 made a similar attempt by measuring the heat produced in the compression of air; but both of these methods involved the assumption, which was only justified by Joule's experiments of 1845, that all the mechanical energy spent in compressing the air was used in producing change of temperature. Mayer states (Leibig, Annalen, 1842) that he has raised the temperature of water from 12° C. to 13° C. by agitating it, but without indicating the force employed or the precautions requisite to secure an accurate result. Joule devised his own method, and carried out the experiments to a satisfactory conclusion. The great paper of V. Helmholtz, ‘Ueber die Erhaltung der Kraft,’ which did so much to extend the new views, was published in 1847.
In 1852 a Royal medal was awarded by the council of the Royal Society to Joule for his researches. He had been elected a fellow on 6 June 1850, and in 1860 he received the Copley medal from the hands of Sir Edward Sabine for the same experiments. In presenting this Sir Edward said: ‘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 manner their sense of the special ​and original character and high desert of Mr. Joule's discovery.’
The summary already given is not by any means a complete account of Joule's activity. In 1848, in a paper entitled ‘Some Remarks on Heat and on the Constitution of Elastic Fluids’ (Phil. Mag. 4th ser. vol. xiv.; Collected Papers, i. 290), he determined, according to the molecular theory of gases, the velocity of a molecule of hydrogen under a pressure of one atmosphere, and about the same time he calculated the ratio in which, according to the theoretical correction of Laplace, Newton's value for the velocity of sound required to be increased. The result of this calculation (‘On the Theoretical Value of Sound,’ Phil. Mag. 3rd ser. vol. xxxi.; Collected Papers, i. 282) was to bring up Newton's theoretical value from 943 to 1095 feet per second. The value given by Newton's measurements was 1130.
The results of some experiments on the air-engine (Phil. Trans. 1852, pt. i.; Collected Papers, i. 331) were communicated to the Royal Society on 19 June 1851, and about the same time the important series of papers ‘On the Thermal Effects experienced by Air in rushing through Small Apertures’ (Phil. Mag. 4th ser. Suppl. vol. iv.; Collected Papers, ii. 216) and ‘On the Thermal Effects of Fluids in Motion’ (Phil. Trans. 1853; Collected Papers, ii. 231) was commenced in conjunction with Sir William Thomson. Joule's earlier experiments had shown that when air is allowed to expand into a vacuum there is on the whole neither loss nor gain of heat. According to these more accurate investigations there is a very slight cooling effect produced by the expansion of both air and carbonic acid, while with hydrogen a slight heating effect is observed. These results are in satisfactory accord with Thomson's thermo-dynamic reasoning, as developed in his paper already referred to. The experiments were carried out in part in one of the cellars of his house in Acton Square, Salford, and afterwards in a large yard attached to his father's brewery, New Bailey Street, Salford.
This series of papers was followed by an investigation into ‘Some Thermo-dynamic Properties of Solids’ (Phil. Trans. 1859; Collected Papers, i. 413), in which, at the suggestion of Sir William Thomson, the changes in temperature produced by longitudinal extension and compression of various solids were examined; the anomalous behaviour of indiarubber had already been noted by Gough, and careful experiments were made on this point. In 1860 a paper was read ‘On the Surface Condensation of Steam’ (Phil. Trans. 1861; Collected Papers, i. 502).
The experiments on the value of J., as determined by the heating of a wire, required for their completion an accurate means of measuring an electric current. For this purpose a new electric current meter was invented, which consisted of a coil of wire suspended from the arm of a balance between two fixed coils (Collected Papers, i. 584). The same principle is adopted at present in Sir William Thomson's balance instruments and in the standard Ampère meter of the Board of Trade. When using the tangent galvanometer to measure a current, an accurate value of the magnetic force due to the earth is required, and this led Joule to examine the methods ordinarily employed, and to suggest modifications and improvements. These are contained in papers ‘On an Apparatus for determining the Horizontal Intensity in Absolute Measure’ (Proc. Manchester Lit. and Phil. Soc. vi. 129; Collected Papers, i. 561), and ‘On a New Magnetic Dip Circle’ (Proc. Manchester Lit. and Phil. Soc. viii. 171; Collected Papers, i. 575), with experiments on magnets (ib. i. 589).
In his earlier years Joule made various experiments on magnetism with Dr. Scoresby, while about 1845 he was engaged with Dr. (now Sir) Lyon Playfair in various researches on the change of volume occurring on solution, and the relation in volumes between simple bodies, their oxides and sulphurets (Memoirs of the Chemical Society, vols. i. ii. and iii.; Collected Papers, ii. 11, 117, 173, 180). The third of the above papers contains the account of his experiments on the temperature at which the density of water is a maximum.
Joule's work sufficiently indicates the breadth of his interests and the greatness of his powers. His papers were collected by the Physical Society of London, under his own editorship, and appeared in two volumes; the first contains his own papers, the second those published by him jointly with others (Joule, Scientific Papers, vol. i. 1885, vol. ii. 1887). He was to have been president of the British Association at the Bradford meeting in 1872, and again at the Manchester meeting in 1887, but ill-health prevented his attendance on both occasions. In 1872 his health gave way, and from that time till his death on 11 Oct. 1889 he lived quietly at his residence, 12 Wardle Road, Sale, pursuing his studies so far as his health permitted. His modesty was always notable. ‘I believe,’ he told his brother on 14 Sept. 1887, ‘I have done two or three little things, but nothing to make a fuss about.’ During the later years of his life he received many distinctions both English and foreign. He was created LL.D. ​ of Dublin in 1857, D.C.L. of Oxford in 1860, and LL.D. of Edinburgh in 1871. In 1878 he was granted a civil list pension of 200l., and in 1880 the Albert medal of the Society of Arts was presented him by the Prince of Wales.
There is an oil-painting by George Patten, painted in 1863, in the rooms of the Manchester Literary and Philosophical Society, and another, painted in 1882 by the Hon. John Collier, in the possession of the Royal Society. A bust was executed by George Reynolds in 1882. A statue by Mr. Alfred Gilbert, R.A., was placed (1893) by public subscription as a companion to Chantrey's statue of Dalton in Manchester town-hall, and a memorial tablet was admitted to Westminster Abbey directly beneath the memorial of Darwin.
Joule married, on 18 Aug. 1847, Amelia, daughter of John Grimes, comptroller of customs at Liverpool. She died in 1854, leaving a son and daughter.
R. T. G.