WILLIAM GILBERT (1540-1603)

1600 – England

‘Gilbert’s principal area of study related to magnetism, however, his method of enquiry is equally significant’

portrait of WILLIAM GILBERT ©

WILLIAM GILBERT

Gilbert rejected the scholastics’ approach to science, preferring the experimental method, which he applied to the Earth’s magnetic properties.
He carried out some of the first systematic studies of the lodestone in Europe and showed that the Earth acts as a bar magnet with magnetic poles.

His celebrated text, ‘De magnete, magnetisque corporibus, et de magno magnete tellure‘ (On the Magnetic, Magnetic Bodies and the Great Magnet Earth – 1600) is considered to be one of the first truly scientific texts.
Gilbert received his medical training in Cambridge and practiced as a physician in London. He became president of the College of Physicians and was physician to Queen Elizabeth I.

In the time of Elizabeth I and Shakespeare, England was still largely a place of superstition and religious fervor. Gilbert concurred with Copernicus, a potentially dangerous sentiment in an era when elsewhere in Europe others such as Giordano Bruno and later GALILEO were being persecuted (and in the case of Bruno, executed) for sharing the same opinion.


Magnetism was to cast its influence in the eighteenth century, displayed through the electric fluid of GALVANI and VOLTA
.

He distinguished the properties of magnetism from the attractive effect produced by friction with amber. In so doing he introduced the term that was to become electricity.
He introduced a number of expressions to the English language including: magnetic pole, electric force and electric attraction.
A term of magneto motive force, the gilbert, is named after him.

Gilbert and others postulated that magnetism is the force holding the planets in their orbits.

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JOHANNES KEPLER (1571-1630)TIMELINE

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PIETER VAN MUSSCHENBROEK (1692-1761) EWALD JURGEN VON KIELEL (1700- 48)

1745 – Holland/Germany

‘Electricity produced by electrostatic machines can be stored in a jar’

The Leyden Jar

diagram of the use of the 'LEYDEN JAR'

In modern terms the Leyden jar is a capacitor or condenser.
In 1734 Stephen Gray (c.1666-1736), an English experimenter, discovered that electric charge could be conducted over distance. He also classified various substances into conductors and insulators of electricity. He suggested that metals were the best conductors and thus introduced the use of electric wire.

In 1734 Musschenbroek, a professor from Leyden in Holland discovered that electricity could be stored in a jar of water.
During the same year, von Kleist, a German scientist also discovered the same principle independently.
In later versions of what became known as the Leyden jar, water was replaced by copper foil inside and outside the jar.
The Leyden jar became a novelty and in village faires magicians used ‘electricity in a bottle’ to amaze and entertain villagers.

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BENJAMIN FRANKLIN (1706-1790)

1752 – The New World

Portrait of BENJAMIN FRANKLIN ©

BENJAMIN FRANKLIN

‘If you would not be forgotten when you are dead and rotten, either write things worth reading, or do things worth writing about’

Curious about how just about everything works, from governments to lightning rods, Franklin’s legacy, in addition to the many inventions such as lightning conductors, bifocal lenses and street lamps, was one of learning. He established one of the first public libraries as well as one of the first universities in America, Pennsylvania. He established the Democratic Party. Franklin was one of the five signatories of the Declaration of Independence from Great Britain in 1776 and was a later participant in the drafting of the American Constitution.

‘Benjamin Franklin’s choice for the signs of electric charges leads to electric current being positive, even though the charge carriers themselves are negative — thereby cursing electrical engineers with confusing minus signs ever since.
The sign of the charge carriers could not be determined with the technology of Franklin’s time, so this isn’t his fault. It’s just bad luck’

Franklin was a pioneer in understanding the properties and potential of electricity. He undertook studies involving electric charge and introduced the terms ‘positive’ and ‘negative’ in explaining the way substances could be attracted to or repelled by each other according to the nature of their charge. He believed these charges ultimately cancelled each other out so that if something lost electrical charge, another substance would instantly gain the same amount.

 

His work on electricity climaxed with his kite flying experiment of 1752. In order to prove lightning to be a form of electricity, Franklin launched a kite into a thunderstorm on a long piece of conducting string. Tying the string to a capacitor, which became charged when struck by lightning, vindicated his theories.

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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.

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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 ©

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.

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HANS CHRISTIAN OERSTED (1777-1851)

1820 – Denmark

‘Electric current produces a magnetic field’

drawn portrait of HANS CHRISTIAN OERSTED ©

Oersted discovered that an electric current could make the needle of a magnetic compass swivel. It was the first indication of a link between these two natural forces. Although Oersted discovered electromagnetism he did little about it. This task was left to AMPERE and FARADAY.

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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

GEORG OHM


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