NATURE 



617 



THURSDAY, OCTOBER 26, if 



SCIENTIFIC WORTHIES 

 XX.— James Prescott Joule 

 TAMES PRESCOTT JOULE was born at Salford on 

 J Christmas-Eve of the year 181S. His father and 

 his grandfather before him were brewers, and the busi- 

 ness, in due course, descended to Mr. Joule and his elder 

 brother, and by them was carried on with success till it 

 was sold in 1S54. Mr. Joule's grandfather came from 

 Elton, in Derbyshire, settled near Manchester, where he 

 founded the business, and died at the age of fifty-four in 

 1799. His father, one of a numerous family, married a 

 daughter of John Prescott of Wigan. They had five 

 children, of whom James Prescott Joule was the s& ond, 

 and of whom three were sons — Benjamin, the eldest. James, 

 and John, and two daughters — Alice and Mary. Mr. 

 Joule's mother died in 1836 at the age of forty-eight ; and 

 his father, who was an invalid for many years before his 

 death, died at the age of seventy-four in the year 1858. 



Young Joule was a delicate child, and was not sent to 

 school. His early education was commenced by his 

 mother's half-sister, and was carried on at his father's 

 house, Broomhill, Pendlebury, by tutors, till he was about 

 fifteen years of age. At fifteen he commenced working in 

 the brewery, which, as his father's health declined, fell 

 entirely into the hands of his brother Benjamin and 

 himself. 



Mr. Joule obtained his first instruction in physical 

 science from Dalton, to whom his father sent the two 

 brothers to learn chemistry. Dalton, one of the most 

 distinguished chemists of any age or country, was then 

 president of the Manchester Literary and Philosophical 

 Society, and lived and received pupils in the rooms of the 

 Society's House. Many of his most important memoirs 

 were communicated to the Society, whose Transactions 

 are likewise enriched by'a large number of communi- 

 cations from his distinguished pupil. Dalton's instruc- 

 tion to the two young men commenced with arithmetic, 

 algebra, and geometry. He then taught them natural 

 philosophy out of Cavallo's text-book, and afterwards, 

 but only for a short time before his health gave way in 

 1837, chemistry from his own " New System of Che- 

 mical Philosophy." "Profound, patient, intuitive," his 

 teaching must have had great influence on his pupils. 

 We find Mr. Joule early at work on the molecular consti- 

 tution of gases, following in the footsteps of his illustrious 

 master, whose own investigations on the constitution of 

 mixed gases, and on the behaviour of vapours and gases 

 under heat, were among the most important of his clay, 

 and whose brilliant discovery of the Atomic Theory 

 revolutionised the science of Chemistry and placed him 

 at the head of the philosophical chemists of Europe. 



Under Dalton, Mr. Joule first became acquainted with 

 physical apparatus ; and the interest excited in his 

 mind very soon began to produce fruit. Almost imme- 

 diately he commenced experimenting on his own account. 

 Obtaining a room in his father's house for the purpose, 

 he began by constructing a cylinder electric machine in a 

 very primitive way. A glass tube served for the cylinder ; 

 Vol. xxvi. — No. 678 



a poker hung up by silk threads, as in the very oldest 

 forms of electric machine, was the prime conductor ; 

 and for a Leyden jar he went back to the old historical 

 jar of Cunoeus, and used a bottle half filled with water, 

 standing in an outer vessel, which contained water also. 



Enlarging his stock of apparatus, chiefly by the work 

 of his own hands, he soon entered the ranks as an 

 investigator, and original papers followed each other in 

 quick succession. The Royal Society List now contains 

 the titles of ninety-seven papers due to Joule, exclusive 

 of over twenty very important papers detailing researches 

 underta! en by him, conjointly with Thomson, with Lyon 

 Playfair, and with Scoresby. 



Mr. Joule's first investigations were in the field of 

 magnetism. In 1838, at the age of nineteen, he con- 

 structed an electro-magnetic engine, which he described 

 in Sturgeon's " Annals of Electricity " for January of that 

 year. In the same year and in the three years following 

 he constructed other electro-magnetic machines and 

 electro-magnets of novel forms ; and experimenting with 

 Ihe new apparatus, he obtained results of great import- 

 ance in the theory of electro-magnetism. In 1840 he 

 discovered, and determined the value of the limit to 

 the magnetisation communicable to soft iron by the 

 electric current ; showing for the case of an electro- 

 magnet supporting weight, that when the exciting current 

 is made stronger and stronger, the sustaining power tends 

 to a certain definite limit, which, according to his esti- 

 mate, amounts to about 140 lbs. per square inch of either 

 of the attracting surfaces. He investigated the relative 

 values of solid iron cores for the electro-magnetic 

 machine as compared with bundles of iron wire; and, 

 applying the principles which he had discovered, he pro- 

 ceeded to the construction of electro-magnets of much 

 greater lifting power than any previously made, while he 

 studied also the methods of modifying the distribution of 

 the force in the magnetic field. 



In commencing these investigations he was met at the 

 very outset, as he tells us, with "the difficulty, if not impos- 

 sibility, of understanding experiments and comparing them 

 with one another which arises in general from incomplete 

 descriptions of apparatus, and from the arbitrary and 

 vague numbers which are used to characterise electric 

 currents. Such a practice," he says, " might be tolerated 

 in the infancy of science ; but in its present state of 

 advancement greater precision and propriety are im- 

 peratively demanded. I have therefore determined," he 

 continues, "for my own part to abandon my old quantity 

 numbers, and to express my results on the basis of a unit 

 which shall be at once scientific and convenient." 



The discovery by Faraday of the law of electro- 

 chemical equivalents had induced him to propose the 

 voltameter as a measurer of electric currents ; but the 

 system proposed had not been used in the researches 

 of any electrician, not excepting those of Faraday 

 himself. Joule, realising for the first time the import- 

 ance of having a system of electric measurement which 

 would make experimental results obtained at different 

 times and under various circumstances comparable 

 among themselves, and perceiving at the same time 

 the advantages of a system of electric measurement, 

 dependent on, or at any rate comparable with the 

 chemical action producing the electric current, adopted 



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