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Coulombs 1787 Newtonian force law:The Electrical PendulumStill in Advanced TextbooksFeynmanRestaging Coulombs LegacyThe“restaging”of Coulombs torsion balance brought forward a number of issues dealing with precision,acceptance,rethoric,replicability,luck!Restaging Coulombs LegacyFeynman:The Torsion Balance is not preciseRestaging Coulombs LegacyFeynman:Corroboration of the inverse square law is established through Gausss law and the corresponding zero field in a(not necessarily spherical)conductor.Restaging Coulombs LegacyFeynman:Coulombs law is wrongHermeneutical“Coulombian”Circle!Textbook Physics Corroborates HistoryHistory Corroborates Textbook PhysicsAre other circles possible?Let us try aHermeneutical“Voltaic”Circle!Force and Tension:A comparison of the Torsion Balance and the ElectrometerTension for the electrometer:Voltas devicesVolta against CoulombTorsion for tension:Kelvins elecrometersCoulomb and the Newtonian forcesThe torsion balance and the electrical pendulumThe corroboration of Coulombs lawIs it a fundamental law?Force and Tension:A comparison of the Torsion Balance and the ElectrometerNot so different after all:both based on repulsive electrical forces in equilibrium,in one case with elastic torsion,in the second case with weight.The measurement of forces or tensions largely depends on the theoretical backgroundTorsion for TensionKelvins Electrometers show that the two instruments are not intrinsecally differentVolta refused Coulombs lawWhat did he want to quantify?Volta wanted to measure a tension force,an effort to push outwards;but mostly he wanted to measure a tendency(intensity,tension)towards equilibrium and thus a quantity that tends to diminish approaching equilibrium.Newtons force does not diminish towards equilibrium,but Leibniz vis mortua doesVoltas in-tension is better understood in a Scholastic and Leibnitian context1782:Contributions towards the discovery of water compositionParis experiments with Lavoisier and Laplace 1783:Analogies,Heat1786-89:Electrometers and Electrometry;Electrical Meteorology1790:Eudiometric Measurements1792:Contact Electricity between MetalsMemoria seconda(14 May):“E la diversit de metalli che fa”A bimetallic arch acts also on nerves alone,and on the tongueTransunto(June),Memoria terza(November):Metals“veri motori di elettricit”First class conductors(metals)of different kind have an electromotive power that is generated in the contact point between them and the second class conductors(liquids)1793:Airs Dilatation Coefficient at Constant Pressure 1794:Waters Vapour TensionVoltas Theory:1783 Caloreil calore tende continuamente ad espandersi;che si diffonde,e comunica dai corpi pi caldi ai meno caldi,fino a tanto,che si venga ad unazione equilibrata,cio,che sian ridotti essi corpi ad una temperatura egualeil calore,per linnata sua tendenza allequilibrio,si distribuisce ne corpi a proporzione della loro capacitun altro esempio tratto dallelasticit dellaria,la quale pu in certa qual manieraVoltas Theory:1783 Calorerappresentare lespansibilit del calore,per cui tende egualmente,che quella allequilibrio.Lesempio,che abbiamo preso dallelasticit dellaria,avremmo potuto prenderlo egualmente dalla velocit,che si comunica da un corpo allaltro per mezzo del semplice urto,dallelettricit,che si propaga da uno in altro conduttore per ricomporsi ad equilibrio ec.e in generale da ogni cosa,che si riparte,e si distribuisce giusta le stesse leggi di equilibrioFactorisationTutto avrebbe stabilita,e confermata questa proposizione:che le capacit rispettive di due corpi sono in ragione reciproca delle mutazioni,che soffrono in pi o meno,merc quel riparto,che li conduce ad uno stato di azione equilibrataC1DTDT1=C2D DT2Voltas theoretical works:InterdisciplinarityWe know that Volta did not confine himself to electricity,but that he dealt at the same time with heat,pneumatics and chemistryIs his concept of in-tension confined to electricity or is it common to all fields of his researches?FactorisationVoltas Theory:1778-80 Saggio Teorico e Sperimentaleanalogia fuoco-fuoco elettrico affinit,ossia forze attrattive delle minime parti di ciascun corpo verso il nostro fluidoforze mutue attrattive distinte dalla universale gravitazionecapacit:il fluido non gi ripartito nella semplice ragione delle masse e dei volumi;ma in ragione delle rispettive forze attraentiVoltas Theory:1784 Lezioni Compendioselo stato,ossia lintensione dellelettricitEgli facile il concepire,che lazione dellelettricit,in ragione composta della sua intensit,e della capacit de conduttoriVoltas research programmeFor Volta the electric fluid is one and in a state of equilibrium,that is neutral.This depends on the mutual forces between the particles of the body and the fluid,forces that are balanced.When this state of equilibrium is modified,for instance through friction,because of the unbalance,an electric charge is perceived(accumulation or diminution of fluid)that tends to regain the equilibrium state.This tension is characteristic of the body and depends on its capacity to store charges according to the relation Q=CT.Voltas research programmeThe tension tends to expell charges(excess of fluid)towards other bodies,in a different state.If(conducing)bodies are in contact,the charge is divided in relation to the capacity of the bodies.If a discharge is produced,the effect depends both on the tension and on the quantity of charge.Moreover the tension(?the charge)produces an electrical atmosphere(a sphere of activity)that acts at(great)distances and thus diminishes with the inverse of the distance and not with the inverse square.Voltas research programmeThis in turn produces an unbalance in the electrical fluid of the bodies immersed in this atmosphere,an actuation(induction)is produced,and these bodies acquire a potential electricity,and thus a tension.Charges of opposite sign face each other and an attraction follows.On the basis of this attraction principle all the electrical phenomena can be explained,keeping in mind the tension(expandibility of the fluid)and the actuation produced by the atmospheres.Voltas research programmeWhen instead charges of the same sign face each other the tension(and the consequent attraction)manifests itself towards other bodies(including air)and thus the apparent effect of repulsion is attributed to these attraction towards other directions.Voltas research programme Summarising Volta introduces two quantities:not only the total amount of the“quality”(charge)but also the state of the body(its tension).One extensive(additive)and the other in-tensive(non additive)related together through the specific capacity of the bodies to store the extensive quantity.Thus the intensive quantity is given by the ratio between the extensive one and the capacity(“volume”):T=Q/CVoltas research programmeThe same relation connecting Charge,Capacity and Tension can be applied to Heat(fire,caloric fluid),to the air and to the quantity of motion.In other words if we have definite quantities of some“qualities”that are conserved during the process,the state of these quantities is characterized by a tendency towards equilibrium that depends on the capacity of the body that stores the given quantity.A small capacity(extension),implies a great in-tension towards equilibrium.Voltas research programmeThus a quantification of qualities is achieved.Capacity is extensive(additive)as the quality it refers to,in-tension instead is intensive(non additive).The product of the intensive factor by the extensive factor is a constant depending on the various situations.Voltas research programmeThis kind of approach,even if Volta does not outlines the effects of the riequilibrium of the fluids(of the qualities)and he does not introduce the concept of work(about to be born)is linked to principles of equilibrium,cause-effect,conservation,to tendencies to reestablish the perturbed equilibrium,through the actuation of potential(virtual)qualities.There are no references to Cartesian mechanicism,nor to Newtonian forces.Rather a scholastic terminology mediated by Leibniz and Boscovich.Voltas research programmeObviously I am not pre-dating the formulation of energy conservation:Voltas conserved quantities are usually substances(electric fluid,heat,air)and not functions(except perhaps in the case of quantity of motion),obviously again there is no conversion(of substances!)but extended use of analogiesBut,as usual,this is not the end of the story The Galvani-Volta debate:chronologyGalvani1781 1o Esperimento1786 2o Esperimento1791-2 Commentarius1794 3o Esperimento1797 MemorieVolta1792 Prime reazioni1792 Teo spec.contatto1795 Teo gen.contatto1797 Elettrom.cond1799 Pila1801 Identit due fluidiGalvani:1781 Primo EsperimentoContrazioni in presenza di scaricheGalvani:1786 Elettric.atmosfericaRana come elettrometroGalvani:1786 2 EsperimentoContrazioni senza scaricheGalvani:1786 2 EsperimentoArchi“conduttori”,elettricit animaleGalvani:1786 2 EsperimentoInterpretazione:muscoli come bottiglie di Leyda Galvani:1791-2 Il“De Viribus”Galvani:1791-2 Il“De Viribus”Diviso in 4 parti1.Contrazioni con elettricit artificiale(primo esperimento)2.Contrazioni con elettricit atmosferica 3.Ipotesi elettricit animale,contrazioni con arco monometallico,maggiori contrazioni con archi bimetallici(secondo esperimento)4.Tesi elettrofisiologiche basate sullelettricit animale Galvani:1791-2 Il“De Viribus”Volta:1792 Prime ReazioniPrima memoria(24 marzo-5 maggio):Dallincredulit al fanatismo al dubbioa)Accettazione elettricit animale e archi“conduttori”b)Due metalli necessari per contrazioni con animali interic)Ipotesi metalli“elettromotori”d)Spiegazione alternativa del primo esperimento di Galvani:atmosfere immaterialiVolta:1792 Teoria speciale del contattoMemoria seconda(14 maggio):“E la diversit de metalli che fa”;Arco bimetallico agisce sui soli nervi,sulla lingua Transunto(giugno),Memoria terza(novembre):i metalli“veri motori di elettricit”I conduttori di prima classe(metalli)di specie diverse hanno un potere elettromotore che si genera nel punto di contatto tra essi e i conduttori di seconda classe(umidi)1792Galvani:1794 Terzo EsperimentoContrazioni senza metalliVolta:1795 Teoria generale del contatto“E la diversit de conduttori che necessaria”Terza lettera a Vassalli(7 ottobre):“Esse(esperienze)mostrano soltanto,che sono io andato troppo innanzi asserendo,che non si potrebbe mai collapplicazione di soli conduttori umidi,ossia di 2a classe,senza lintervento cio di alcun metallo o conduttore di 1a classe,eccitare le convulsioni nelle rane”Galvani:1797 Memorie a Spallanzani“Egli vuole questa elettricit la stessa che quella comune a tutti i corpi;io,particolare e propria dellanimale:egli pone la causa dello sbilancio negli artifizi che si adoprano,e segnatamente nella differenza dei metalli;io,nella macchina animale:egli stabilisce tal causa accidentale ed estrinseca;io,naturale ed interna:egli in somma tutto attribuisce ai metalli,nulla allanimale;io,tutto a questo,nulla a quelli,ove si consideri il solo sbilancio”Un confronto谢谢你的阅读v知识就是财富v丰富你的人生谢谢！
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