LOUIS DE BROGLIE (1892-1987)

1924 – France

‘The wave-particle duality of matter.
Like photons, particles such as electrons also show wave-particle duality, that is, they also behave like light waves’

Einstein had suggested in one of his 1905 papers that the ‘photoelectric’ effect could be explained by an interpretation that included electromagnetic waves behaving like particles. De Broglie simply reversed the argument and asked: ‘if waves can behave like particles (a stream of quanta or photons), why should particles not behave like waves?’

Louis de Broglie (1892-1987), French physicist. De Broglie was instrumental in showing that waves and particles can behave like each other at a quantum level (wave-particle duality). He suggested that particles, such as electrons, could behave as waves. This was confirmed by Davisson and Germer in 1927. He was awarded the 1928 Nobel Prize for Physics for his work.


By applying quantum theory de Broglie was able to show that an electron could act as if it were a wave with its wavelength calculated by dividing PLANCK‘s constant by the electron’s momentum at any given instant. His proposal was found to be plausible by experimental evidence shortly afterwards.

BORN, SCHRODINGER and HEISENBERG offered arguments to the debate. NIELS BOHR provided some context in 1927 by pointing out that the equipment used in experiments to prove the case one way or another greatly influenced the outcome of the results. A principle of ‘complementarity’ had to be applied suggesting the experimental proof to be a series of partially correct answers, which have to be interpreted side by side for the most complete picture. Uncertainty and Complementarity together became known as the ‘Copenhagen interpretation’ of quantum mechanics.

Eventually, the ‘probabilistic’ theories of Heisenberg and Born largely won out. At this juncture, cause and effect had logically been removed from atomic physics and de Broglie, like Einstein and Schrödinger, began to question the direction quantum theory was taking and rejected many of its findings.

picture of the Nobel medal - link to nobelprize.org

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LEON FOUCAULT (1819- 68)

1850 – France

portrait of LEON FOUCAULT (seated) ©

LEON FOUCAULT  (Smithsonian)

‘A Foucault pendulum is a simple pendulum – a long wire with a heavy weight (bob) at the end – except that at the top it is attached to a joint which allows it to swing in any direction’

Foucault’s pendulum proved that the Earth is rotating

Once a Foucault pendulum is set in motion, it seems not to swing back and forth in the same direction but to rotate. In fact, it is the rotation of the Earth beneath the pendulum which gives rise to its apparent rotation.
The angle of rotation per hour, which is constant at any particular location, can be calculated from the formula 15 sin Φ, where Φ is the geographical latitude of the observer. At the North or South Pole, the pendulum would rotate through 360 degrees once a day. At the equator it would not rotate at all.

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1888 – France

‘When a system in equilibrium is subjected to a change in conditions, it adjusts itself so as to try to oppose that change’

photo portrait of HENRI LOUIS LE CHATELIER ©

The principle is a consequence of the law of conservation of energy.

Le Chatelier’s principal is valuable in understanding how to control the industrial production of chemicals such as ammonia.
Nitrogen and hydrogen react to form ammonia. When the pressure of this system is increased, more ammonia is produced, but when the pressure is lowered, ammonia is decomposed into hydrogen and nitrogen. Thus by controlling pressure and temperature, ammonia can be produced with the minimum of waste.

Le Chatelier was a chemist and is remembered for inventing thermocouples for measuring high temperatures (1877) and oxyacetylene welding (1895).

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LOUIS PASTEUR (1822- 95)

1865 – France

‘Many human diseases have their origin in micro-organisms’

1862 – ‘Memoire sur les corpuscles organises qui existent dans l’atmosphere’ (Note on Organized Corpuscles that exist in the Atmosphere) – Puts an end to centuries of debate on the theory of spontaneous generation.

Although a chemist, Pasteur is best remembered for his contributions to medicine. His name is used to describe the process of ‘pasteurisation’.
Pasteur proved that living microorganisms cause fermentation. Previously scientists had assumed that fermentation was a chemical process.
Pasteur showed that the alcohol in fermentation was made by the yeast microbe. He also realised that when fermentation went wrong it was due to other germs.

In 1863 he showed that brief, moderate heating of wine and beer kills germs, thereby sterilizing the foodstuffs and ending the fermentation process. The process now known as pasteurisation is still used in the food industry.

His investigations led him to believe that microorganisms could also cause disease in humans. Pasteur realized the dangers of infection, but the English surgeon JOSEPH LISTER (1827-1912) is credited with developing and systematizing the notion of antiseptic surgery so that operations could be made safer if an ‘antiseptic’ procedure was introduced to destroy microbes and curb the infections that followed wounds or surgery.

In 1876, Pasteur confirmed the findings of ROBERT KOCH’s discovery of the anthrax bacillus. After EDWARD JENNER’s breakthrough in the development of vaccination against smallpox, little had been done to take advantage of the potential of this treatment against other disease.

In 1882 Pasteur successfully applied his discovery of vaccination by attenuated culture of microorganisms to anthrax and in 1885 to the treatment of rabies in humans.

On 14 November 1888 the Pasteur Institute opened in Paris.

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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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1827 – France

‘Two current-carrying wires attract each other if their currents are in the same direction, but repel each other if their currents are opposite.
The force of attraction or repulsion (magnetic force) is directly proportional to the product of the strengths of the currents and inversely proportional to the square of the distance between them’

portrait of ANDRE AMPERE ©


Another addition to the succession of ‘inverse-square’ laws begun with NEWTON’s law of universal gravitation.
Ampere had noted that two magnets could affect each other and wondered, given the similarities between electricity and magnetism, what effect two currents would have upon each other. Beginning with electricity run in two parallel wires, he observed that if the currents ran in the same direction, the wires were attracted to each other and if they ran in opposite directions they were repelled.

He experimented with other shapes of wires and generalised that the magnetic effect produced by passing a current in an electric wire is the result of the circular motion of that current. The effect is increased when the wire is coiled. When a bar of soft iron is placed in the coil it becomes a magnet. This is the solenoid, used in devices where mechanical motion is required.

Ampere exploited OERSTED’s work, devising a galvanometer which measured electric current flow via the degree of deflection upon its magnetic needle.

He attempted to interpret all his results mathematically in a bid to find an encompassing explanation for what later became referred to as electromagnetism (Ampere had at that time christened it electrodynamics), resulting in his 1827 definition.

Ampere’s name is commemorated in the SI unit of electric current, the ampere.

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1808 – France

‘Volumes of gases which combine or which are produced in chemical reactions are always in the ratio of small whole numbers’

One volume of nitrogen and three volumes of hydrogen produce two volumes of ammonia. These volumes are in the whole number ratio of 1:3:2

N2 + 3H2 ↔ 2NH3

Along with his compatriot Louis Thenard, Gay-Lussac proved LAVOISIER’s assumption, that all acids had to contain oxygen, to be wrong.

portrait of GAY-LUSSAC ©


Gay-Lussac re-examined JACQUES CHARLES’ unpublished and little known work describing the effect that the volume of a gas at constant pressure is directly proportional to temperature and ensured that Charles received due credit for his discovery.

Alongside JOHN DALTON, Gay-Lussac concluded that once pressure was kept fixed, near zero degrees Celsius all gases increased in volume by 1/273 the original value for every degree Celsius rise in temperature. At 10degrees, the volume would become 283/273 of its original value and at – 10degrees it would be 263/273 of that same original value. He extended this relation by showing that when volume was kept fixed, gas would increase or decrease the pressure exerted on the outside of the gas container by the same 1/273 factor when temperature was shifted by a degree Celsius. This did not depend upon the gas being studied and hinted at a deep connection shared by all gases. If the volume of a gas at fixed pressure decreased by 1/273 for every 1degree drop, it would reach zero volume at -273degrees Celsius. The same was true for pressure at fixed volume. That had to be the end of the scale, the lowest possible temperature one could reach. Absolute zero.

In an 1807 gas-experiment, Gay-Lussac took a large container with a removable divider down the middle and filled half with gas and made the other half a vacuüm. When the divider was suddenly removed, the gas quickly filled the whole container. According to caloric theory, temperature was a measure of the concentration of caloric fluid and removal of the divider should have led to a drop in temperature because the fluid was spread out over a greater volume without any loss of caloric fluid. (The same amount of fluid in a larger container means lower concentration).
Evidence linking heat to mechanical energy accumulated. Expenditure of the latter seemed to lead to the former.

Gay-Lussac was an experimentalist and his law was based on extensive experiments. The explanation of why gases combine in this way came from AVOGADRO.

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