4. First case study – the subdivision of the light - HM Treasury

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F05 Ch4 Subdivision of the light.doc 05/04/2006 19:34:00 Technological roulette – a multi-disciplinary study of the dynamics of innovation in electrical, electronic and communications engineering. 4. First case study – the subdivision of the light when one of the limbs was touched with a scalpel. Galvani later observed a similar reaction in legs which were hung by copper skewers from an iron rail. It fell to Allessandro Volta to give the correct explanation for this phenomenon, viz. that the contact between dissimilar metals gave rise to an electrical potential which acted as a stimulus for the muscular action. Volta went on to devise a practical means of utilising this effect – his couronne des tasses, a battery consisting of a number of cups containing a saline solution into which were dipped plates of zinc and silver. The silver plate of one cup was connected to the zinc plate of the next cup, the terminal zinc and silver plates of the battery serving as a source from which a continuous electrical current could be drawn. He subsequently constructed his pile consisting of alternating plates of dissimilar metals separated by discs of moistened material. The results of Volta’s research were communicated in a letter to Sir Joseph Banks, President of the Royal Society of London and read by him to the Society on 26th June 1800, Houston 1894,p107 stimulating a host of inventions and discoveries in the field of electrochemistry. In 1801, Humphry Davy was appointed as the director of the laboratory of the Royal Institution which had been founded by Count Rumford two years earlier. He used a Voltaic pile to perform electrolysis on a wide variety of chemical compounds. Davy’s brother noted Davy 1836, p446 that among these early experiments were several investigations of luminous properties of the electric current. These were recorded in a 65 Fig. 4.5 Volta’sCouronne des tasses Fig. 4.6 Volta’s pile from Phil Trans Roy Soc (1800) Fleming1921 Jarvis 1955a
F05 Ch4 Subdivision of the light.doc 05/04/2006 19:34:00 Technological roulette – a multi-disciplinary study of the dynamics of innovation in electrical, electronic and communications engineering. 4. First case study – the subdivision of the light Fig. 4.7 Sir Humphry Davy demonstrates the electric arc at the Royal Institution From Scientific American 29 March 1884 paper entitled “An Account of Some Experiments on Galvanic Electricity made in the Theatre of the Royal Institution.” “The apparatus employed in these experiments was composed of 150 series of plates of copper and zinc of 4 inches square, and 50 of zinc and silver of the same size. The metals were carefully cemented into four boxes of wood in regular order, after the manner adopted by Mr. Cruickshank, and the fluid made use of was water combined with about 1/100 part of its weight of nitric acid.” “The shock taken from the batteries in combination by the moistened hands, was not so powerful but that it could be received without any permanently disagreeable effects. Charges were readily communicated by means of them to coated jars, and to a battery; but in this case the effects produced by the electricity were much less distinct than in the case of immediate application.” “When the circuit in the batteries was completed by means of small knobs of brass, the spark perceived was of a dazzling brightness, and in apparent diameter at least 1/8 of an inch. It was perceived only at the moment of the contact of the metals, and it was accompanied by a noise or snap.” “When instead of the metals, pieces of well-burned charcoal were employed, the spark was still larger and of a vivid whiteness, an evident combustion was produced, the charcoal remained red hot for some time after the contact and threw off bright corruscations.” “Four inches of steel wire 1/170 of an inch in diameter, on being placed in the circuit became intensely white hot at the point of connection, and burnt with great vividness being at the same time red throughout the whole of their extent.” Collected Works of Sir Humphry Davy Vol. 11 p211 Davy was not satisfied with his results and persuaded patrons of the Royal Institution to subscribe for a huge battery made of 2000 individual cells. This was 66 Jehl 1937
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4. First case study – the subdivision of the light - HM Treasury

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