Henry Cavendish (1731–1810)As a fellow-scientist wrote, Henry Cavendish possessed a clarity of comprehensionand an acuteness of reasoning that have been the lot of very fewof his predecessors since the days of Newton. At home and abroad he wasregarded as the most distinguished British man of science of his day. Amonghis many achievements are the demonstration of the existence of hydrogenas a distinct substance, the demonstration that water is a compound and thedetermination of the density of the earth. He was also one of the pioneersof electrical research, presaging much of the work of Coulomb, Faraday andOhm. Clerk Maxwell, who edited some of his papers, was fascinated byhis character: ‘Cavendish cared more for investigation than publication. Hewould undertake the most laborious researches in order to clear up a difficultywhich no-one but himself could appreciate, or was even aware of. Andwe cannot doubt that the result of his enquiries, when successful, gave hima certain degree of satisfaction. But it did not excite in him that desire tocommunicate the discovery to others which, in the case of ordinary men ofscience, generally ensures the publication of their results.’Lord Charles Cavendish, the third son of the second Duke ofDevonshire, married Lady Anne Grey, the fourth daughter of Henry, Dukeof Kent. She was living in Nice, owing to frail health, when her first child Henry was born onOctober 10, 1731. A second child, Frederick, was bornin England two years later, but their mother died shortly afterwards. Littleis known of the early years of the two boys, except that they attendedthe Hackney Academy, a London school well thought of in its day for theeducation of children of the upper classes in sound classical learning. Eachof the brothers went up to the University of Cambridge, matriculated as anobleman and resided there for four years, but left without taking a degree.The college to which they belonged was St Peter’s, commonly known asPeterhouse. Shortly after the younger brother had left Cambridge they madethe customary tour on the continent; apart from Paris, it is not known wherethey went. Henry may well have studied mathematics and physics when hewas in Paris. The brothers did not have much to do with each other later inlife, although they remained on good terms.After returning to England, Henry Cavendish went to live with hisfather at a house in Great Marlborough Street, in the Soho district of London,and apparently continued to do so until his father died. It was during thisperiod of almost thirty years that he carried out the fundamental electricalresearch which so impressed Clerk Maxwell. He began his research careerby assisting his father, a gifted experimental physicist, who was a prominentfellow of the Royal Society. Lord Charles made some valuable investigationsinto heat, electricity and terrestrial magnetism. Franklin remarked that ‘Itwere to be wished that this noble philosopher would communicate more ofhis experiments to the world, as he makes many, and with great accuracy.’Lord Charles was not a wealthy man but the financial allowance hemade to his eldest son was so small as to be described as niggardly by contemporaries.It is not known just where the money came from, but, in 1783,
when his father died, or even before, Henry Cavendish became extremelywealthy, apparently through a succession of legacies from relatives. However,by this time he had become accustomed to living parsimoniously.His large library of scientific works, housed in Bedford Square, was opento any serious scholars. At one time it was in a somewhat neglected state,so, having been told of a German scholar in straitened circumstances whowas capable of classifying the books in a satisfactory manner, Cavendisharranged for him to act as his librarian; in return Cavendish gave him theprincely sum of £10 000, with which to purchase an annuity. He could beremarkably generous when he felt so inclined.Cavendish’s principal residence was a large villa at Clapham, then justa village south of London. Most of its rooms were equipped with scientificapparatus. It was at Clapham that he made his discovery of the composition of water andmeasured by means of a torsion balance the density of the earth.There was a ladder up a large tree in the garden, from the top of which hemade astronomical and meteorological observations. He was very much aman of habit, invariably dining off leg of mutton and taking exactly the samewalk every day on his own. His pathologically shy and nervous disposition,on which anyone who had any contact with Henry Cavendish was apt toremark, has been attributed to his comparative poverty during the first fortyyears of his life.In appearance Cavendish was tall and thin, his face intelligent andmild. His voice was hesitant and somewhat shrill. He retained the dressof his youth – faded violet suit with high collar, frilled shirt-wrists and aknocker-tailed periwig. Each year on a fixed day his tailor provided him witha new suit that was a replica of the old one. When out-of-doors he was tobe seen wearing a three-cornered hat. He would often be accompanied bySir Charles Blagden, who for seven years acted as his assistant. As secretaryof the Royal Society, Blagden made frequent visits to the continent, usuallyto Paris, where he was a friend of Berthollet and Laplace, amongst others, andcourted the lively widow of Antoine Lavoisier. When eventually Cavendishparted with Blagden’s services he provided him with an annuity of £500 andleft him a legacy of £15 000 in his will.Cavendish’s interests extended over a wide field of natural philosophy,and every subject of investigation was subjected to a rigorous quantitativeexamination. The results he obtained with simple methods and apparatuswere amazing. He was not only a highly skilled experimentalist but alsoa capable mathematician. In common with others in England during thisperiod, he employed the methods of Newton, for example the fluxionalnotation for differentiation. In chemistry he adhered to the old calorictheory of heat, although the experiments he performed were helping toundermine it. Like Newton, he had a deep dislike of controversy. As a resulthe published remarkably little; for example only two research papers onelectricity, although, when Clerk Maxwell was editing Cavendish’s electricalresearches for publication, after his death, he found twenty packages fullof manuscripts on mathematical and experimental electricity.
The vast bulk of the Cavendish papers must have given Maxwellpause, but, once he had begun, he found them fascinating. Cavendish hadquietly presaged many of the important results of the following century. Hehad performed some extraordinarily accurate experiments with the crudestof equipment, using a pair of pithballs, on strings, which repelled each otherto measure charge and his own body to measure resistance. In going through the papers Maxwellfound many of the experiments mentioned so originalthat they seemed worth repeating, checking or improving. Cavendishhad done his experiments by making himself part of the electric circuitand noticing how intense the electric shocks he felt under different circumstanceswere. To check his conclusions he would summon his servantRichard to replace him and then observe his servant’s reactions. Visitorsto his laboratory were often pressed into taking part instead of Richard;Cavendish offended a visiting American physicist, who refused to act as aguinea pig and went off saying ‘when an English man of science comes tothe United States we do not treat him like that’.Although Franklin’s work had been published twenty years earlier,Cavendish’s paper ‘An attempt to explain some of the principal phenomenaof electricity by means of an elastic fluid’ involves basically the same idea,but gives it a mathematical treatment, quantitative rather than qualitative.Both Cavendish and Franklin served on a committee of the Royal Societyto report on the best way of protecting buildings from lightning; they recommendedthe installation of pointed conductors. However, others were infavour of blunt ends, and George III agreed.Anotorious controversy erupted,with political overtones, since pointed ends were thought somehow to beunpatriotic.Although Cavendish mainly lived as a recluse owing to a morbiddislike of society, he nevertheless participated in the intellectual life ofLondon. He was a member of the Royal Society of Arts, a trustee of theBritish Museum, a fellow of the Society of Antiquaries, a manager of theRoyal Institution and a foreign associate of the Paris Academy. Like hisfather, he was prominent in the Royal Society, to which he was electedin 1760, served on the Council and some of its committees; and regularlyattended the Dining Club, to which he often brought guests. They wereadvised that it was useless to try to engage him in conversation on anynon-scientific topic. The only known portrait of him, now in the BritishMuseum, was drawn surreptitiously at one of the club dinners.Henry, later Lord, Brougham recalled seeing him at a Royal SocietyConversazione and hearing ‘the shrill cry he uttered as he shuffled quicklyfrom room to room, seeming to be annoyed if looked at, but sometimesapproaching to hear what was passing among others. His walk was quickand uneasy. He probably uttered fewer words in the course of his life thanany man who lived to fourscore years, not at all excepting the monks of LaTrappe.’ Of the many stories told about his idiosyncrasies, one concerns adistinguished foreign scientist who said that he wished to meet ‘one of the greatest intellectualornaments of this country, and one of the most profound
philosophers of all time’. Cavendish was so embarrassed that he wasreduced to total silence and escaped in his carriage at the first opportunity.Cavendish made a number of journeys by carriage within Britain,always in the summer, when conditions of travel were least difficult, andgenerally accompanied by Blagden. Although usually their main purposewas to visit other men of science, generally some scientific work was doneen route; for example they studied the variation of barometric pressure withaltitude, or collected specimens of minerals to be examined at leisure ontheir return. They inspected many of the places where science was beingapplied in industry, as the industrial revolution began to gather momentum.Often the people he met were later guests of his at the Royal Society DiningClub.Cavendish died on February 24, 1810, at the age of seventy-eight,and was buried in All Saints Church, Derby, now designated the cathedral,where his famous ancestor Bess of Hardwick had built an elaborate tombfor herself. Owing to his frugal life-style, he had accumulated a fortune ofover a million pounds, a huge sum in those days; he was one of the richestmen in England. When he died none of this wealth went directly to supportscientific research; he believed that it should return to the family fromwhich it came. However, many years later the University of Cambridge benefitedfrom the generosity of the Cavendish family through the endowmentof the Cavendish Professorship of Experimental Physics and the CavendishLaboratory.Charles Augustin Coulomb (1736–1806)The end of the Thirty Years War left France the most powerful nation inEurope. Although the golden age of French science was yet to come, someremarkable physicists were already distinguishing themselves before theend of the ancien r ´egime. One of the first was Coulomb, the subject of ournext profile. He has been described as the complete physicist, rivalled inthe eighteenth century only by Henry Cavendish, combining experimentalskill, accuracy of measurement and great originality with mathematicalpowers adequate to all his demands. He invented the torsion balance andused it to show that the force between electrically charged particles is proportionalto the product of their charges and inversely proportional to thedistance between them. This fundamental result is known as Coulomb’slaw; the unit of electrical charge is also named after him.