"School of Athens" Fresco in Apostol...

School of Athens” Fresco in Apostolic Palace, Rome, Vatican City, by Raphael 1509 – 1510 (Photo credit: Wikipedia)



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    GEORG SIMON OHM (1789-1854)

    1827 – Germany

    ‘The electric current in a conductor is proportional to the potential difference’

    In equation form, V = IR, where V is the potential difference, I is the current and R is a constant called resistance.

    greek symbol capital ohm (480 x 480)

    Ohm’s law links voltage (potential difference) with current and resistance and the scientists VOLTA, AMPERE and OHM.

    Ohm is now honoured by having the unit of electrical resistance named after him.
    If we use units of VI and R, Ohm’s law can be written in units as:

    volts = ampere × ohm

    photograph of george simon ohm © + diagram of simple electric circuit


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    NEXT button - ANDRE MARIE AMPERE (1775-1836)TIMELINE


    LEONHARD EULER (1707- 83)

    1755 – Switzerland

    ‘Analytical calculus – the study of infinite processes and their limits’

    Swiss mathematician. His notation is even more far-reaching than that of LEIBNIZ and much of the mathematical notation that is in use to-day may be credited to Euler.

    The number of theorems, equations and formulae named after him is enormous.
    Euler made important discoveries in the analytic geometry of surfaces and the theory of differential equations.

    Euler popularised the use of the symbol ‘Π‘ (Pi); e  , for the base of the natural logarithm; and i , for the imaginary unit.
    Euler is credited with contributing the useful notations  f (x) , for the general function of x ; and  Σ , to indicate a general sum of terms.

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    THOMAS MALTHUS (1766-1834)

    1798 – England

    ‘If unchecked, the human population would grow geometrically while the food supply could only grow arithmetically. In two centuries the population would be to the food supply 256:9’

    (in an arithmetic series of numbers there is a common difference between any number and its successor, while in a geometric series each number is a constant multiple of the preceding number)

    When Malthus, an obscure country curate, published his Essay on the Principle of Population it excited much attention and placed its author in the centre of a controversial political debate on population. The essay was denounced as unholy, atheistic and subversive of the social order. FRIEDRICH ENGELS, the cofounder of communism, criticised Malthus’ essay for underestimating science;

    But science increases as fast as population – in the most normal conditions it also grows in geometrical progression – and what is impossible for science?

    Portrait of Thomas Malthus ©


    Malthusian ideas form the foundations of the modern theory on the relationship between economics, population and the environment. DARWIN wrote in his book ‘The Origin of Species’ that his theory ‘is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms’.

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    JAMES WATT (1736-1819)

    1765 – Glasgow, Lanarkshire, UK

    ‘Steam engine’

    Watt’s steam engine was the driving force behind the industrial revolution and his development of the rotary engine in 1781 brought mechanisation to several industries such as weaving, spinning and transportation.

    Portrait of JAMES WATT who developed the steam engine ©


    Although THOMAS NEWCOMEN had developed the steam engine before Watt was even born, Newcomen’s machines had been confined to the world of mining.

    In 1764, when Watt was asked to repair a scale model of Newcomen’s engine he noted its huge inefficiency. The heating and cooling of the cylinder with every stroke wasted huge amounts of fuel; and wasted time in bringing the cylinder back up to steam producing temperature, which limited the frequency of strokes. He realised that the key to improved efficiency lay in condensing the steam in a separate container – thereby allowing the cylinder and piston to remain always hot. Watt continued to improve his steam engine and developed a way to make it work with a circular, rotary motion. Another of his improvements was the production of steam under pressure, thus increasing the temperature gap between source and sink and raising the efficiency in a manner later described by SADI CARNOT and elucidated by JAMES JOULE.



    RICHARD ARKWRIGHT was the first to realise the engine could be used to spin cotton, and later in weaving. Flour and paper mills were other early adopters, and in 1788 steam power was used to paddle marine transportation. In the same year, Watt developed the ‘centrifugal governor’ to regulate the speed of the engine and to keep it constant.

    diagram of the Watt 10hp engine

    Watt 10hp engine

    Watt was the first to coin the term ‘horsepower’, which he used when comparing how many horses it would require to provide the same pull as one of his machines. In 1882 the British Association named the ‘watt’ unit of power in his honour.

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    LUIGI GALVANI (1737- 98) ALESSANDRO VOLTA (1745-1827)

    1791 & 1799 – Italy

    ‘Galvani: An electric current is produced when an animal tissue comes into contact with two different metals.

    Volta: An electric current is not dependent on an animal tissue and can be produced by chemicals’

    Galvani was wrong and Volta was right.

    Galvani had found that by touching a dead frog’s legs with two different metal implements, the muscles in the frog’s legs would twitch. Galvani wrongly concluded it was the animal tissue that was storing the electricity, releasing it when touched by the metals. He felt he had discovered the very force of life – ‘animal electricity’ – that animated flesh and bone.

    portrait of LUIGI GALVANI ©


    Soon dozens of scientists were trying to bring corpses back to life by electrifying them. Volta was not convinced the animal muscle was the important factor in the production of the current.

    He repeated Galvani’s experiments and concluded, controversially at the time, the different metals were the important factor.

    A bitter dispute arose as to whose interpretation was correct. Volta began putting together different combinations of metals to see if they produced any current; later he produced a wet battery of fluid and metals. Volta’s method of producing electric current involved using discs of silver and zinc dipped in a bowl of salt solution. He reasoned that a much larger charge could be produced by stacking several discs separated by cards soaked in salt water – by attaching copper wires to each end of the ‘pile’ he successfully obtained a steady current.

    The ‘voltaic pile’ was the first battery in history (1800). Napoleon Bonaparte, who at the time controlled the territory in which Volta lived, was so impressed he made him a Count and awarded him the Legion d’Honour.

    portrait of ALESSANDRO VOLTA ©


    Volt, the SI unit of electric potential, honours Volta.

    Although Galvani’s theory on ‘animal electricity’ was not of any major importance, he has also achieved nominal immortality; like ‘volt’, the words ‘galvanic’ (sudden and dramatic), ‘galvanised’ (iron or steel coated with zinc) and ‘galvanometer’ (an instrument for detecting small currents) have become part of everyday language.

    A volt is defined as the potential difference between two points on a conductor carrying one ampere current when the power dissipated between the points is one watt.

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