INDEX

"School of Athens" Fresco in Apostol...

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

TIMELINE

  • THE FIRST MILLENIUM

saints,sisters and sluts + scientists header
 
 

MAIN INDEX

NEXT buttonTHE SCIENTIFIC METHOD

  • << top of page
  • Advertisements

    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

    GEORG OHM


    Wikipedia-logo © (link to wikipedia)

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

    NEXT buttonELECTRICITY

    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 ©

    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’.

    Wikipedia-logo © (link to wikipedia)

    NEXT buttonTIMELINE

    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 ©

    JAMES WATT

    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_by_Mather_Brown_1790

    RICHARD ARKWRIGHT

    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.

    Wikipedia-logo © (link to wikipedia)

    HENRY CAVENDISH (1731-1810)TIMELINE

    HEATHEAT

    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 ©

    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 ©

    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.

    Wikipedia-logo © (link to wikipedia)

    NEXT buttonTIMELINE

    NEXT buttonELECTRICITY

    CHARLES DE COULOMB (1736-1806)

    1785 – France

    ‘The force of attraction or repulsion between two charges is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them’

    The region around a charged object where it exerts a force is called its electric field. Another charged object placed in this field will have a force exerted on it. Coulomb’s rule is used to calculate this force.

    Coulomb, a French physicist, made a detailed study of electrical attractions and repulsions between various charged bodies and concluded that electrical forces follow the same type of law as gravitation. Coulomb found a similar principle linking the relationship of magnetic forces. He believed electricity and magnetism, however, to be two separate ‘fluids’.
    It was left to HANS CHRISTIAN OERSTED, ANDRE-MARIE AMPERE and MICHAEL FARADAY to enunciate the phenomenon of electromagnetism.

    The SI unit of electric charge, coulomb (C), one unit of which is shifted when a current of one ampere flows for one second, is named in his honour.

    He also articulated Coulomb’s rule of friction, which outlines a proportional relationship between friction and pressure.

    Wikipedia-logo © (link to wikipedia)

    NEXT buttonTIMELINE

    NEXT buttonELECTRICITY

    CAROLUS LINNAEUS (1707- 78)

    1735 – Sweden

    ‘A system for naming organisms by assigning them scientific names consisting of two parts’

    Portrait of Linnaeus ©

    LINNAEUS

    Each species is given a two-word Latin name – The genus name that comes first and begins with a capital letter, and the species name, which begins with a lower case letter. The genus name is often abbreviated, and the names are always written in italics or underlined. The Linnaean system has six classification categories – in descending order, kingdoms, phyla, classes, orders, genera and species. Only two are used for naming organisms.

    German botanist Rudolph Camerarius (1665-1721) had shown that no seed would grow without first being pollinated. In 1729, Linnaeus wrote in a paper about ‘the betrothal of plants, in which …..the perfect analogy with animals is concluded’. He insisted that it is the stamens where pollen is made (the ‘bridegrooms’) and the pistils where seeds are made (‘the brides’) that are the sexual organs, and not the petals as had been considered previously.

    As botanists and zoologists looked at nature, or ‘Creation’, there was no way of classifying the animal kingdom depicted in bestiaries of the time but alphabetically; or of distinguishing the real from the mythical.

    Linnaeus developed a system of classification that had two key features. Starting with the plant kingdom, Linnaeus grouped plants according to their sexual organs – the parts of the plant involved in reproduction. Each plant species was given a two-part Latin name. The first part always refers to the name of the group it belongs to, and the second part is the species name.

    Linnaeus divided all flowering plants into twenty-three classes according to the length and number of their stamens – the male organs, – then subdivided these into orders according to the number of pistils – female organs, – that they possessed. A twenty-fourth class, the Cryptogamia, included the mosses and other non-flowering plants.

    illustration of flower reproductive structures ©

    Many people were offended by the sexual overtones in Linnaeus’s scheme. One class he named Diandria, meaning ‘two husbands in one marriage’, while he said ‘the calyx might be regarded as the labia majora; one could regard the corolla as the labia minora’. For almost a century, botany was not seen as a decent thing for young-ladies to be interested in.

    Linnaeus’s scheme was simple and practical and in 1745 he published an encyclopedia of Swedish plants, when he began considering the names of species. Realizing he had to get the names in place before someone else gave plants other names, he gave a binomial label to every known plant species and in 1753 published all 5,900 in his Species Plantarium.

    Believing his work on the plant kingdom complete, he turned his attention to the animal kingdom. In his earlier Systema Naturae of 1735, he had used the classification ‘Quadrupeds’ (four-legged creatures) but replaced this with Mammals, using the presence of mammary glands for suckling young as a more crucial distinguishing characteristic. The first or prime group in the Mammals was the primates, which included Homo sapiens (wise man). His catalogue of animals was included in the tenth edition of Systema Naturae, listed with binomial names.

    By the time Linnaeus died it was the norm for expeditions around the world to take a botanist with them, hence CHARLES DARWIN’s famous voyage on the Beagle.

    Wikipedia-logo © (link to wikipedia)

    Wikispecies-logo ©

    NEXT buttonTIMELINE