Electrochemistry, Past and Present - American Chemical Society

Chapter 4

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James Prescott Joule, Electricity, and the Equivalent of Heat Stella V. F. Butler Greater Manchester Museum of Science and Industry, Castlefield Manchester M3 4JP, United Kingdom James Prescott Joule is best known for his determination of the mechanical equivalent of heat. Joule began his scientific career by investigating electrical phenomena. Joule was fascinated by the possibilities that electromagnets might become useful as sources of industrial power. He designed and built various electro-magnetic engines, trying to understand how to produce maximum efficiency. He began to link together electricity, heat and mechanical power by observing their transformations. His investigations culminated in his quantification of the dynamical equivalent of heat. Joule lived and worked in an industrial community; his concern about "power" was shared by many others who derived income from manufacturing. His success in developing a conceptual framework about energy owed much to his considerable experimental skills. At the 1847 annual meeting of the British Association for the Advancement of Science (BAAS), in Oxford, James Prescott Joule, a young Salford-born brewer, presented a paper in which he demonstrated that heat must be regarded as an equivalent form of mechanical "force" or, what we could call, "energy". (1) Four years previously, at the Cork meeting of the BAAS, he had begun by showing that the work done to drive a magneto-electric engine could be converted by means of the electric current into the equivalent amount of heat. (2) Despite the implications of Joule's conclusions for the interpretation of nature and especially his assertion that heat was simply another form of "force" and not, as many still held, a material substance, his presentation in Oxford did not arouse much interest. However, William Thomson, who had been appointed Professor of Natural Philosophy at Glasgow University the year before, was impressed by Joule's experimental work and his ideas. (3) The two men discussed his paper and thus began one of the most important friendships in the history of science. 0097-6156/89/0390-0050$06.00/0 © 1989 American Chemical Society

In Electrochemistry, Past and Present; Stock, John T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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4. BUTLER

J. P. Joule, Electricity, and the Equivalent of Heat

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Joule's work provided important experimental proofs for Thomson's exposition of the laws of thermodynamics published between 1851-1855. (4) Indeed in the opening passage to his paper on the mechanism of electrolysis, Thomson maintained "certain principles discovered by Mr. Joule .... must ultimately become an important part of the foundation of the mechanical theory of chemistry". (5) To a certain extent Joule's presentation to the BAAS in 1847 and his lecture at St. Ann's Church School the previous month represent the end point in his investigations concerning the relationships between various physical "forces" notably electricity, heat, and mechanical power. Joule was not, of course, alone in speculating about the nature of heat. As Thomas Kuhn has outlined, between 1842 and 1847 three other individuals, Mayer, Colding and Helmholtz also presented similar hypotheses. (6) Others also speculated on the concept of energy or "force" as a unifying heuristic tool for understanding natural phenomena. There were a number of reasons why these philosophers presented similar hypotheses at this period, including in many cases, a "Naturphilosophen" approach in which the organism is used as a fundamental metaphor for understanding the natural world. In this paper I focus specifically on the development of Joule's ideas by examining his experimental work. The sequence of investigations through which he formulated his theories underline the importance of his enthusiasm for electrical phenomena and, in particular, magneto-electricity. By examining both Joule's published work and his apparatus, part of which survives in the Joule Collection of the Greater Manchester Museum of Science and Industry, the considerable experimental skill involved in determining the equivalent values becomes clear. We are also able to chart the changing style of his scientific work, and can begin to relate his method of work to his developing theories about natural phenomena. A Fascination for Magnets James Prescott Joule was born in Salford in 1818. (7) His father owned a brewing business from which the family derived considerable wealth. James, a delicate child with a minor spinal deformity was educated at home with his elder brother Benjamin. Between 1833 and 1837, the two boys were taught maths and science by the venerable John Dalton. The following year, 1838, Joule's first researches were published in the Annals of Electricity. He described different forms of electro-magnetic engines, his aim to design a more efficient and powerful machine. (8) Annals had been established as a scientific periodical in 1836 by William Sturgeon who moved to Manchester in 1838 to set up the Royal Victoria Gallery of Practical Science. (9) Joule's interest in electro-magnetism was stimulated by this self-taught man who, in 1825 had demonstrated the first softiron electromagnet at the Society of Arts in London. (10) The Royal Victoria Gallery was a speculative venture which did not enjoy long term success. Nevertheless, Sturgeon clearly drew around himself a group of enthusiasts for electro-magnets whose designs were exhibited at the Gallery. Joule also lectured there in February, 1841 "On a New Class of Magnetic Forces". (11)



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Joule, like many others, envisaged electricity as a source of industrial power: in May 1839 he wrote "I can hardly doubt that electro-magnetism will ultimately be substituted for steam to propel machinery". (12) He therefore set about investigating the relationship between the current used to create the magnet and the strength of magnetic attraction. (13) He designed, made, and calibrated delicate galvanometers. He then measured the relationship between the strength of the magnet and the size of the current, establishing that the magnetic attraction is proportional to the square of the electric current and the square of the length of the wire. The similarities between the formula he deduced and the laws of gravitational attraction no doubt appealed to him. This work was typical of Joule's experimental style - he was always concerned to devise accurate and sensitive measuring instruments and always interested in the mathematical relationships between phenomena. By 1841 however, Joule's optimism regarding the industrial potential of his electromagnets had diminished. In his lectures at the Victoria Gallery in February he described the simple rules he had found to hold true of his electro-magnetic engines - that the "duty" which, for Joule was a measure of the efficiency of the machine, is proportional to the intensities of the battery, and that what he called the "magneto-electric resistance" produced by the rotation of the bars, (the back emf) acts against the battery current which consequently reduces the magnetism of the bars. (14) At certain velocities therefore the force is so reduced that the bars are no longer accelerated. He concluded "I almost despair of the success of electro-magnetic attractions as an economical source of power" (15) - for, his electro-magnetic engines simply did not compare to the fuel efficiency of steam engines: without vastly more efficient batteries Joule could not see how to improve his machine. Heat and Electricity A few months before this lecture Joule had presented his first experiments on the relationship between heat and electricity. He simply placed coils of different kinds of wire in jars of water and measured the change in temperature. This work represents a shift away from his concern about improving and inventing gadgets and a growing interest in measurable phenomena, most notably electricity. Just as he had looked for simple mathematical relationships to understand magnetisation so he sought patterns in the quantities of heat and electricity which he was able to measure. In his first communication he maintained that "the calorific effects of equal quantities of transmitted electricity are proportional to the resistance opposed to its passage whatever may be the length, thickness, shape or kind of metal which closes the circuit". (16) Although, at this stage his work gave no opposition to the caloric theory which conceived of heat as a fluid, Joule in presenting ideas about magnetism, maintained that atoms were surrounded by atmospheres of electricity and magnetism; the skewing of these atmospheres explained electrical and magnetic phenomena. The vibration of the magnetic atmospheres "is called heat and will of course, increase in violence and extent with the increase of temperature of the bar". (17)



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Although Joule used the term "caloric" value of heat he, like many of his contemporaries, never thought in earlier nineteenth century terms of "caloric" as a material substance. (18) By August 1841, Joule could report on further investigations into heat and electricity. (19) This time he wrapped the conducting wire around a glass tube which was then placed in a jar of water. This apparatus has survived and is illustrated in Fig.1. Using sensitive galvanometers and thermometers he established that the heat evolved is proportional to the resistance of the conducting wire and the square of the "electric intensity" (current). Faraday had previously noted the heating effects of the electric current and had speculated on the relationship of the two forces suggesting that they are always "definite in amount". (20) Joule went on in the same paper to look at the heat evolved in the cells of batteries. By the end of 1841 he was beginning to regard the electric current as, fundamentally, a force - he carried out experiments to demonstrate that the heat evolved in "ordinary chemical combination" is the "product of resistance to electric conduction". (21) He maintained that such "phenomena are easily understood if, with the great body of philosophers we keep in view the intimate relation which subsists between chemical affinity and the electric current". (22) In 1832 Faraday had demonstrated the decomposition of water by magneto-electricity, and had gone on to suggest that equivalent weights of chemicals are associated with equal quantities of electricity. (23) For Faraday, as for Joule, electricity represented the combining force of atoms for one another. Joule was elected to the Manchester Literary and Philosphical Society on 25th January, 1842. Later that year, he attended the BAAS meeting which Manchester hosted and presented a paper on his electrical experiments. The BAAS provided Joule with a national audience for his ideas and brought him into contact with others who shared his electrical interests. (24) These included Reverend William Scoresby, vicar of Bradford, who had carried out a number of experiments on electro-magnets. Joule subsequently worked with Scoresby, designing and building an electro-magnetic engine to test its "duty" or efficiency. (25) At the BAAS meeting, Joule described his own combustion experiments before discussing his electrolysis results - he maintained that the heat of chemical reactions resulted from the electrical resistance between the atoms at the moment of their union. (26) Following these experiments, and others on the heat evolved during the electrolysis of water, he began to formulate a theory of heat. He concluded that the heating power of the current produced per chemical equivalent of electrolyte in the battery is proportional to the electromotive force. (27) He had already established in his work on electro-magnetism that the mechanical power of a machine is also proportional to the intensities of the batteries or the electromotive force. He therefore suggested a constant mathematical relationship between the mechanical and heating powers of the current. Before testing this proposition, he maintained that "electricity may be regarded as the grand agent for carrying, arranging and converting chemical heat". (28) At this time he



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Figure 1. Apparatus used by Joule in his 1841 investigation concerning the relationship between heat and electricity. Courtesy of the Greater Manchester Museum of Science and Industry Trust.



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still regarded heat as the "momentum of the atmospheres" of electricity. He went on to explore the relationship between heat and mechanical "force" via the agency of electricity by immersing a small revolving electromagnet in water and measuring the changes in temperature for a given size of current induced in it by rotating it between the poles of another magnet. The little electromagnet was rotated by a system of falling weights. (29) He demonstrated that the heat evolved by the coil was proportional to the square of the current induced by the rotation of the electromagnet. All that had happened was that "force" had been expended and heat generated. He went on to demonstrate that the same effects are observed if the current through the electromagnet is produced by a battery instead of by electromagnetic induction. Having established the equivalence of voltaic and magneto electricity he went on to investigate what happens when you have both in a circuit. In one series the current induced in the electromagnet was used to oppose the current of the batteries, in another it was used to add to the effect of the battery. His results, he maintained were consistent with the "law" he had established earlier that the heat observed is proportional to the square of the current - i.e. there is no special effect observed because of the assistance or resistance which the magneto-electricity presents to the voltaic current. For Joule this was further evidence for the fundamental nature of electricity as a force. Magneto-electricity could, he maintained, generate heat. (30) It was a short step to measuring not only the temperature and the current observed in the electro-magnetic induction experiments but also the mechanical power necessary to turn the apparatus. He used his system of falling weights linked via pulleys and an axle to the magneto-electric machine. He simply calculated the mechanical "force" expended measuring the distance fallen by his (known) weights. The falling weights drove the magneto-electric engine, the current from which generated heat. Having ascertained the force required to produce a particular temperature change, he equated it to the heat evolved, concluding that "the quantity of heat capable of increasing the temperature of a pound of water by one degree of Fahrenheit's scale is equal to and may be converted into a mechanical force capable of raising 838 lbs to the perpendicular height of one foot". (31) This was Joule's first full articulation of the dynamical theory of heat. In a postscript to his paper, presented at the Chemical Section of the British Association meeting in Cork, in August 1843, he elaborated upon his dynamical theory of heat by supporting Count Rumford's assertion that the heat observed when boring cannon results from friction not from a change in the "capacity" of the metal. He went on to modify his views regarding the electrical nature of chemical heat. Previously he had believed that the heat evolved in chemical reactions was due to the electrical current involved in the chemical process. Instead he suggested that heat was the result of the "mechanical force expended by the atoms in falling towards one another." (32) He believed that his propositions would ultimately provide an explanatory framework for the whole of chemistry.


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Further Work on the Mechanical Equivalent of Heat These sets of experiments on the relationship between magnetoelectricity and heat broadened Joule's view of the nature of heat and "force". Until this time, the summer of 1843, all his experiments had involved electrical phenomena. Although he did not abandon this interest, Joule's work began to focus on mechanical force and the possibility of demonstrating its direct equivalence with heat in the absence of the agency of electricity. He investigated the long-observed thermal effects produced when gases are compressed and allowed to expand. (33) He constructed two identical copper receivers into which he compressed air using a condensing pump he constructed for this purpose. From the observations of Erasmus Darwin, Dalton and Cullen before him, Joule realised that he could expect to observe an increase in temperature. He anticipated the effects to be slight and consequently commissioned from John Benjamin Dancer, perhaps the best known of Manchester's instrument makers, thermometers of "extreme sensibility and very great accuracy". (34) Dancer also made Joule a travelling microscope to enable the scale of each thermometer to be precisely etched. According to Joule these instruments represented a significant improvement in sensitivity and accuracy in thermometry in Britain. Previously Joule had bought thermometers from Fastré, the Parisian instrument maker. Joule showed that when compressed air from one cylinder was allowed to expand into an evacuated cylinder the net temperature change was zero. Under these circumstances no net external work is done so no heat is lost. He went on to calculate from the expansion of air a further set of values for the mechanical equivalent of heat which broadly agreed with the electromagnetic experiments. These experiments and, in particular, Joule's concern for very sensitive measuring instruments suggest that he was, to some extent at least, using experiments to prove his theory of the nature of heat. This experimental style contrasts with his earlier, more open-ended approach. By 1847, Joule had further evidence for the generation of heat by mechanical work through the famous paddlewheel experiments. Using falling weights to turn a wheel in a bath of water, he equated the rise in temperature with the friction produced through the force of the falling weight. (35) Again he calculated a value for the mechanical equivalent of heat. Joule repeated these experiments with slight modifications in 1849 and 1878 establishing ever more accurate values for his equivalence. (36) His conclusions were received with sceptism by some. In 1849, the Royal Society refused to publish his assertion that friction was essentially the conversion of mechanical power into heat. In 1847, Joule was able to outline in detail his views on the conservation of forces and their unity in his lecture at St. Ann's Church School. This was published subsequently in the Manchester Courier. (37) Joule maintained that "the most convincing proof of the conversion of heat into living force has been derived from my experiments with the electro-magnetic engine, a machine composed of magnets and bars of iron set in motion by an electrical battery". (38)


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Joule continued to present his views both to his immediate peers within the Manchester scientific community and through both the Royal Society and the BAAS. As we have already noted, at the annual meeting of the BAAS in Oxford he met William Thomson. Although Thomson did not immediately accept Joule's propositions about heat they eventually became an important component in his synthesis of ideas concerning energy.


The Great Experimenter Although by the 1850s he had completed his mechanical equivalent work, Joule continued to undertake a wide range of investigations. In 1861, at the urging of the telegraph engineers Sir Charles Bright and Mr. Latimer Clark, the British Association set up a committee to consider the need to establish a unit for electrical resistance and to decide the best form in which a standard could be kept. (39) Joule joined the committee the following year. Resistance was first measured in absolute units (cm and seconds) by James Clerk Maxwell, Balfour Stewart and Fleeming Jenkin. Joule's electrical heating law (current squared times resistance) coupled with his accurate determination of the mechanical equivalent of heat provided a vital check on the accuracy of this work. There was good, but not complete agreement. Joule therefore set out to determine the dynamical equivalent of heat. (40) The slight difference persisted. It was finally found by Lord Rayleigh and his group at Cambridge, that Maxwell, Balfour Stewart and Fleeming Jenkin were in error while H.A. Rowland, in the States, showed that Joule's final result (772.55 ft lbs per BThU) had to be increased slightly due to his reliance on glass thermometers. Joule demonstrated his genius for instrumentation during this investigation by developing a current balance - a horizontal flat coil was suspended by the current carrying wire between two fixed coils. The current could be determined by measuring the forces required to counterbalance the attractive or repulsive force experienced by the suspended coil. An instrument similar in design was used by Rayleigh in 1882 and also by the Laboratoire Central d'Eléctricité, Paris to determine the absolute value of current. Although this current balance does not survive, the Joule Collection does contain a number of pieces of apparatus, some dating from the early part of Joule's career. His passion for electromagnets is well demonstrated by the range of magnets. These include a pair made in 1839 to investigate whether any advantage could be gained by using a core made up of wires instead of a solid piece of iron (see Figure 2 ) . The electromagnet constructed to give "great lifting-power" also survives. (41) From these relatively crude but, by Joule's accounts, effective pieces of apparatus we can also gain some insight into the process of his endeavour. For him, science clearly involved engineering skills. His "laboratory" was as much a workshop with furnace and lathe as an area for delicate experimentation. In 1845 Joule could assure William Scoresby with whom he collaborated on a number of experiments on the "duty" or efficiency of electromagnets of the availability of steel wire, wrought iron tubing and copper wire which he sometimes ordered ready covered with



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Figure 2. Electromagnets constructed by Joule to investigate the difference in effect between a solid core and a core made up of iron wires. Courtesy of the Greater Manchester Museum of Science and Industry Trust.



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cotton. (42) Joule clearly suffered few financial constraints to his experimenting and could obtain all he needed from Manchester's engineering suppliers. He was very proud of his magnets in 1851 he applied via the Royal Manchester Institution to exhibit an electro-magnet in the Great Exhibition. (43) As well as the cruder pieces of apparatus, the collection also contains finely crafted instruments including a travelling microscope, specially constructed for Joule by John Benjamin Dancer. Dancer moved to Manchester from his home in Liverpool in 1841. (44) He had been apprenticed originally as an instrument maker to his father from whom he inherited the family business in 1835. Subsequently he went into partnership with A. Abraham, a very successful Liverpool instrument maker with the agreement that the young Dancer would move to Manchester to set up a branch of the firm. Dancer worked very closely with Joule. During 1844 Joule joined Dancer in his "workshop .... every morning for sometime until we completed the first accurate thermometers which were ever made in England". (45) This close relationship between maker and customer was fostered in Manchester by a relatively open scientific community. Joule and Dancer undoubtedly met socially at the Lit and Phil as well as at lectures or conversaziones at the Royal Manchester Institution. Dancer also made several of the instruments Joule required for the long series of experiments on atomic volume he carried out in conjunction with Lyon Playfair. (46) Both Playfair and Dancer were close friends of John Mercer, (47) a manufacturing chemist from Oakenshaw, Lancashire, who was responsible for inventing the process of treating cotton with strong alkali to ensure a good uptake of dye, which continues to bear his name. This remarkable group of scientific talent shared a concern to investigate observable phenomena and demonstrated exceptional ability for inventing new gadgets and chemical processes. However, the collection is not confined to objects originating from Manchester and Salford. Joule also purchased instruments from London - R. and G. Knight and Watkins and Hill. His papers demonstrate the breadth of his knowledge of scientific literature. He was clearly also well and critically informed about the availability of instruments. Conclusions The 1840 edition of the Encyclopaedia Britannica noted that "there is no branch of science more likely to reward the diligence of the young investigator than that which treats of the electric fluid in animal and vegetable life, its effects upon inorganic matter and its connection with the imponderable agents of light and heat". (48) The Voltaic pile had opened up a range of experimental possibilities after 1800; subsequently the work of Oersted and Faraday had indicated the possibilities of magneto-electricity. Faraday's work captured the imaginations of many enthusiastic investigators. Joule was, therefore, by no means alone in developing strong magnets and electro-magnetic machines. What set Joule apart from his fellow enthusiasts was his fascination with the connections between both magneto and voltaic electricity and the "imponderables" of heat and



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more especially mechanical force. Joule had grown up with, and drew his livelihood from industry. In Manchester, one of Britain's great manufacturing centres, sources of mechanical power were of tremendous importance. It is not surprising that Joule's interest in electricity and in particular in the design of electro-magnetic engines lay partly in their possibility as sources of industrial power. Joule's main investigations on the relationship between electricity, heat and mechanical power were completed by 1847. His early descriptions of his electromagnets indicate the importance of William Sturgeon's influence and the lively group of inventors centred around Manchester's Victoria Gallery of Science. The electromagnets that survive emphasise these links. After 1842 his published work demonstrates his familiarity with the work of other investigators. His apparatus also indicates his knowledge of scientific instruments, both British and French, and his close relationship with John Benjamin Dancer. Joule probably directed the instrument maker with detailed specifications, while Dancer contributed his considerable technical expertise. Bennett has noted that this type of collaboration was relatively new in British science in this period. (49) Close study of Joule's experimental procedures also indicate the meticulous skill which enabled him to obtain very accurate measurements. From his first experiments on the relationship between the strength of a magnet and the strength of the electric current, Joule was concerned to develop very sensitive measuring instruments. He devised galvanometers capable of detecting small differences in current and later thermometers which could measure temperature differences as small as 1/200 F. These concerns for accuracy, quantification using standard units and fine measurement, evident in his work from his first published papers, set Joule aside from his British peers and links him with the next generation of investigators, most notably his friend and colleague William Thomson who became principle advocate for modern thermodynamics based on Joule's ideas of the dynamical theory of heat. Acknowledgments I am very grateful to John Stock for his encouragement to prepare this paper. Donald Cardwell, David Gooding and Neil Brown provided valuable and stimulating comments to earlier drafts. The British Council and the American Chemical Society provided financial support to make possible my involvement in the symposium on electrochemistry. Literature Cited 1. 2.

3.

Joule, J.P. Report of the Ann. Mtg. of the Brit, Assoc. Adv. of Sci. Chem. Sec., 1847, p 55. Joule, J.P. "On the calorific effects of magneto-electricity and on the mechanical value of heat", in Joule, J.P. Collected Papers, Physical Society: London; 1884, vol, 1, pp 123-159. Smith, C.W. "William Thomson and the Creation of Thermodynamics: 1840-1855", Archive Hist. Exact Sci., 1976, 16, 231-288.


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5.


6.

7. 8.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

21. 22. 23. 24.

25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.


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Thomson, W. "On the dynamical theory of heat; with numerical results deduced from Mr. Joule's 'Equivalent of a thermal unit' and M. Regnault's 'Observations on steam'", Trans. Roy. Soc. Edin., 1853, 20, 261-288. Thomson, W., Mathematical and Physical Papers, University Press: Cambridge, 1882-1911; vol. 1, pp 472-289. Kuhn, T. "Energy conservation as an example of simultaneous discovery", in Critical Problems in the History of Science; Clagett, M.,Ed; Wisconsin Press: Wisconsin, 1959; Chapter 11. Reynolds, 0. "Memoir of James Prescott Joule", Proc. Manchester Lit. and Phil. Soc., 1892, 6. Joule, J.P. "A Short Account of the Life and Writings of the Late Mr. William Sturgeon", Mem. Manchester Lit. and Phil. Soc, 1857, 14, 77-83. Cardwell, D. "Science and Technology: The Work of James Prescott Joule", Technology and Culture, 1976, 1/7, 674-687. Joule, J.P. Collected Papers, Physical Society: London, 1884; vol.1, pp 46-53. Ibid., p 14. Ibid., pp 10-14. Ibid., pp 47. Ibid., p 48. Ibid., pp 59-60. Ibid., p 53. S. Brush, The kind of motion we call Heat, New York, 1976; pp 31-32. Joule, J.P. Collected Papers, Physical Society: London 1884; vol. 1, pp 60-81. Faraday, M. Experimental Researches in Electricity (1855), reprinted in Great Books of the Western World: Chicago, 1952; para. 1625. Joule, J.P. Collected Papers, Physical Society: London, 1884; vol. 1, p 82. Ibid., p 90. Report of the Ann. Mtg. of the Brit. Assoc. Adv. Sci., 1832. Morrell, J.; Thackray, A. Gentlemen of Science. Early Years of the British Association for the Advancement of Science; Clarendon Press: Oxford, 1981; p 411. Stamp, T.; Stamp, C. William Scoresby, Arctic Scientist; Caedman of Whitby Press: Whitby, 1976; pp 175-185. Joule, J.P. Collected Papers; Physical Society: London, 1884; vol. 1, pp 102-107. Ibid., p 120. Loc. Cit. Ibid., pp 123-159. Ibid., p 146. Ibid., p 156. Ibid., p 158. Ibid., pp 172-189. Ibid., p 174. Ibid., p 202. Ibid., pp 298-328, 632-657. Ibid., pp 265-276. Ibid., p 279.


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40. 41. 42.


43.

44.

45.

46. 47. 48. 49.

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Reports of Committee on Electric Standards appointed by the British Association for the Advancement of Science; Cambridge University Press: Cambridge, 1913; p xvii. Ibid., p xxi. Joule, J.P. Collected Papers; Physical Society: London, 1884; vol. 1, p 40. Stamp, T.; Stamp, C. William Scoresby, Arctic Scientist; Caedmon of Whitby Press: Whitby, 1976; p 180. Royal Manchester Institution Archives, Letter from J.P. Joule to Manchester Great Exhibition Committee, 30th April, 1850. Manchester Central Reference Library, M6/3/11/9. "John Benjamin Dancer, FRAS 1812-1887, An Autobiographical Sketch", reprinted in Proc. Manchester Lit. and Phil. Soc., 1964-5, 107, 1-27. Ashworth, J.R. "A list of apparatus now in Manchester which belonged to J.P. Joule, FRS with remarks on his Mss, letters and autobiography", Mem. Manchester Lit. and Phil. Soc., 1930-1, 7!5, 105-117, p 112. Joule, J.P.; Playfair, L., in Joule's Collected Papers; Physical Society: London, 1884; vol. 2, pp 11-215. Parnell, E.A. The Life and Labours of John Mercer, FRS, FCS; Longmans: London, 1886. "Electricity" in Encyclopaedia Britannica; A. and C. Black: Edinburgh, 1840; 7th edition, vol. 8. Bennett, J. "Instrument makers and the decline of science in England". In Nineteenth Century Scientific Instruments and their Makers; P.R. de Clercq, Ed.; Rodopi: Amsterdam, 1985; pp 13-27.

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Electrochemistry, Past and Present - American Chemical Society

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