EPICURUS (341 – 270 BCE)

Third Century BCE

EPICURUS

“Epicurus’s philosophy combines a physics based on an atomistic materialism with a rational hedonistic ethics that emphasizes moderation of desires and cultivation of friendships.”

Summarized by the Roman author Lucretius, who wrote ‘On the Nature of the Universe’ in 55 BCE – “The light and heat of the Sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove”. This may be considered as accurate for the time, when most people thought that sight was associated with something reaching out from the eye (EMPEDOCLES) .

Plato wrote of a marriage between the inner light and the outer light.

Euclid worried about the speed with which sight worked. He pointed out that if you close your eyes, then open them again, even the distant stars reappear immediately in your sight, although the influence of sight has had to travel all the way from your eyes to the stars and back again before you could see them.

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IBN SINA (AVICENNA) (980-1037)

‘al Qann fi al-Tibb’ (The Canon of Medicine), also ‘ The Book of the Remedy’

Avicenna lived under the Sammarid caliphs in Bukhara. He identified different forms of energy – heat, light and mechanical – and the idea of a force.

AVICENNA

Before GALEN, scientists describing nature followed the old Greek traditions of giving the definitions and following them up with the body of logical development. The investigator was then obliged merely to define the various types of ‘nature’ to be found. With Galen this procedure was changed.

Instead of hunting for these natures and defining more and more of them, reproducing ARISTOTLE’s ideas, AVICENNA, a Persian physician, planned inductive and deductive experimental approaches to determine the conditions producing observable results.

His tome surveyed the entire field of medical knowledge from ancient times up to the most up to date Muslim techniques. Avicenna was the first to note that tuberculosis is contagious; that diseases can spread through soil and water and that a person’s emotions can affect their state of physical health. He was the first to describe meningitis and realize that nerves transmit pain. The book also contained a description of 760 drugs. Its comprehensive and systematic approach meant that once it was translated into Latin in the twelfth century it became the standard medical textbook in Europe for the next 600 years.

Arabic Canon of Medicine by Avicenna 1632

Avicenna thought of light as being made up of a stream of particles, produced in the Sun and in flames on Earth, which travel in straight lines and bounce off objects that they strike.

A pinhole in a curtain in a darkened room causes an inverted image to be projected, upside-down, onto a wall opposite the curtained window. The key point is that light travels in straight lines. A straight line from the top of a tree some distance away, in a garden that the window of the camera obscura faces onto – passing through the hole in the curtain – will carry on down to a point near the ground on the wall opposite. A straight line from the base of the tree will go upwards through the hole to strike the wall opposite near the ceiling. Straight lines from every other point on the tree will go through the hole to strike the wall in correspondingly determined spots, the result is an upside-down image of the tree (and of everything else in the garden).

He realized that refraction is a result of light traveling at different speeds in water and in air.

He used several logical arguments to support his contention that sight is not a result of some inner light reaching outward from the eye to probe the world around it, but is solely a result of light entering the eye from the world outside – realizing that ‘after-images’ caused by a bright light will persist when the eyes are closed and reasoning that this can only be the result of something from outside affecting the eyes. By effectively reversing the extro-missive theory of Euclid, he formulated the idea of a cone emanating from outside the eye entering and thus forming an image inside the eye – he thus introduced the modern idea of the ray of light.

The idea which was to have the most profound effect on the scientific development of an understanding of the behaviour of light was the thought of the way images are formed on a sunny day by the ‘camera obscura’.

AL HAZEN (c.965-1039)

Born in Basra and working in Egypt under al-Hakim, Abu Ali al-Hassan ibn al-Haytham was one of the three greatest scientists of Islam (along with al-Biruni and ibn-Sina). He explained how vision works in terms of geometric optics and had a huge influence on Western science. He is regarded as one of the earliest advocates of the scientific method.

The mathematical technique of ‘casting out of nines’, used to verify squares and cubes, is attributed to al-Hazen.

Al-Hazen dissented with the J’bir Ayam hypothesis of transmutation, thus providing two different strands for Alchemy in Europe from the Islāmic world.

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MEDICINE

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CHRISTIAN THEOLOGY & WESTERN SCIENCE

The speculative Greek philosophers, considering the great overarching principles that controlled the Cosmos, were handicapped by a reluctance to test their speculations by experimentation.
At the other end of the spectrum were the craftsmen who fired and glazed pottery, who forged weapons out of bronze and iron. They in turn were hindered by their reluctance to speculate about the principles that governed their craft.

WESTERN SCIENCE is often credited with discoveries and inventions that have been observed in other cultures in earlier centuries.
This can be due to a lack of reliable records, difficulty in discerning fact from legend, problems in pinning down a finding to an individual or group or simple ignorance.

The Romans were technologists and made little contribution to pure science and then from the fall of Rome to the Renaissance science regressed. Through this time, science and technology evolved independently and to a large extent one could have science without technology and technology without science.

Later, there developed a movement to ‘Christianise Platonism’ (Thierry of Chartres).

Platonism at its simplest is the study and debate of the various arguments put forward by the Greek philosopher PLATO (428/7-348/7 BCE).
The philosopher Plotinus is attributed with having founded neo-Platonism, linking Christian and Gnostic beliefs to debate various arguments within their doctrines. One strand of thought linked together three intellectual states of being: the Good (or the One), the Intelligence and the Soul. The neo-Platonic Academy in Greece was closed by the Emperor Justinian (CE 483-565) in CE 529.
During the early years of the Renaissance, texts on neo-platonism began to be reconsidered, translated and discoursed.

ARISTOTLE

Aristotle’s four causes from the ‘Timaeus’ were attributed to the Christian God, who works through secondary causes (such as angels).

Efficient Cause – Creator – God the Father

Formal Cause – Secondary agent – God the Son

Material Cause – The four elements: earth, air, fire & water.
Because these four are only fundamental forms of the single type of matter, they cannot be related to any idea of ‘elements’ as understood by modern science – they could be transmuted into each other. Different substances, although composed of matter would have different properties due to the differing amounts of the qualities of form and spirit. Thus a lump of lead is made of the same type of matter (fundamental form) as a lump of gold, but has a different aggregation of constituents. Neither lead nor gold would contain much spirit – not as much as air, say, and certainly not as much as God, who is purely spiritual. ( ALCHEMY )

Final Cause – Holy Spirit

All other is ‘natural’ – underwritten by God in maintaining the laws of nature without recourse to the supernatural.
Science was the method for investigating the world. It involved carrying out careful experiments, with nature as the ultimate arbiter of which theories were right and which were wrong.

Robert Grosseteste (1168-1253) Bishop of Lincoln (Robert ‘Bighead’) – neo-platonic reading of Genesis – emanation of God’s goodness, like light, begins creation. Light is thus a vehicle of creation and likewise knowledge (hence ‘illumination’), a dimensionless point of matter with a dimensionless point of light superimposed upon it (dimensions are created by God). Spherical radiation of light carries matter with it until it is dissipated. Led to studies of optical phenomena (rainbow, refraction, reflection).

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ROGER BACON (1214- 94)

(Doctor Mirabilis) ‘The Marvelous Doctor’

(Franciscan friar) Oxford – 1257

‘Mathematics (The first of the sciences, the alphabet of philosophy, door & key to the sciences), not Logic, should be the basis of all study’

Converted from Aristotelian to a neo-Platonist.

ROGER BACON

The Multiplication of Species; the means of causation (change) radiate from one object to another like the propagation of light.

‘An agent directs its effect to making the recipient similar to itself because the recipient is always potentially what the agent is in actuality.’

Thus heat radiating from a fire causes water placed near the fire,
but not in it, to become like the fire (hot). The quality of fire is multiplied in the water (multiplication of species).

All change may be analysed mathematically. Every multiplication is according to line, angles or figures. This thinking comes from the ninth century al-Kinde and his thoughts on rays and leads to a mathematical investigation into light.

Fear of the Mongols, Muslims and the Anti-Christ motivated the Franciscans. Franciscan neo-Platonism was based on Augustinian thought with a mathematical, Pythagorean, approach to nature. Bacon subscribed to this apocalyptical view, suffered trial and was imprisoned.
The Dominicans chose Aristotle – with a qualitative, non-mathematical approach to the world.

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LEONARDO DA VINCI (1452-1519)

1502 – Florence, Italy

‘In the Renaissance science was reinvented’

VITRUVIAN MAN

Leonardo is celebrated as the Renaissance artist who created the masterpieces ‘The Last Supper’ (1495-97) and ‘The Mona Lisa’ (1503-06). Much of his time was spent in scientific enquiry, although most of his work remained unpublished and largely forgotten centuries after his death. The genius of his designs so far outstripped contemporary technology that they were rendered literally inconceivable.

The range of his studies included astronomy, geography, palaeontology, geology, botany, zoölogy, hydrodynamics, optics, aerodynamics and anatomy. In the latter field he undertook a number of human dissections, largely on stolen corpses, to make detailed sketches of the body. He also dissected bears, cows, frogs, monkeys and birds to compare their anatomy with that of humans.

It is perhaps in his study of muscles where Leonardo’s blend of artistry and scientific analysis is best seen. In order to display the layers of the body, he developed the drawing technique of cross-sections and illustrated three-dimensional arrays of muscles and organs from different perspectives.

Leonardo’s superlative skill in illustration and his obsession with accuracy made his anatomical drawings the finest the world had ever seen. One of Leonardo’s special interests was the eye and he was fascinated by how the eye and brain worked together. He was probably the first anatomist to see how the optic nerve leaves the back of the eye and connects to the brain. He was probably the first, too, to realise how nerves link the brain to muscles. There had been no such idea in GALEN’s anatomy.

Possibly the most important contribution Leonardo made to science was the method of his enquiry, introducing a rational, systematic approach to the study of nature after a thousand years of superstition. He would begin by setting himself straightforward scientific queries such as ‘how does a bird fly?’ He would observe his subject in its natural environment, make notes on its behaviour, then repeat the observation over and over to ensure accuracy, before making sketches and ultimately drawing conclusions. In many instances he would directly apply the results of his enquiries into nature to designs for inventions for human use.

LEONARDO DA VINCI

He wrote ‘Things of the mind left untested by the senses are useless’. This methodical approach to science marks a significant stepping-stone from the DARK AGES to the modern era.

1469 Leonardo apprenticed to the studio of Andrea Verrocchio in Florence

1482 -1499 Leonardo’s work for Ludovico Siorza, the Duke of Milan, included designs for weaponry such as catapults and missiles.
‘Pictor et iggeniarius ducalis ( painter and engineer of the Duke )’.
Work on architecture, military and hydraulic engineering, flying machines and anatomy.

1502 Returns to Florence to work for Pope Alexander VI’s son, Cesare Borgia, as his military engineer and architect.

1503 Begins to paint the ‘Mona Lisa’.

1505-07 Wrote about the flight of birds and filled his notebooks with ideas for flying machines, including a helicopter and a parachute. In drawing machines he was keen to show how individual components worked.

1508 Studies anatomy in Milan.

1509 Draws maps and geological surveys of Lombardy and Lake Isea.

1516 Journeys to France on invitation of Francis I.

1519 April 23 – Dies in Clos-Luce, near Amboise, France.

TIMELINE

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MECHANICS

WILLEBRORD SNELLIUS (1580-1626)

1621 – Holland

WILLEBRORD SNELL

‘During refraction of light, the ratio of the sines of the angles of incidence ( i ) and refraction ( r ) is a constant equal to the refractive index of the medium’

In equation form: n₁sin_i = n₂ sin_r 
where n₁ and n₂ are the respective refractive indices of the two media.

The refractive index of a substance is a measure of its ability to bend light. The higher the number the better light is refracted. The refractive index of diamond, 2.42, is the highest of all gems.

Refraction is the change in direction of a ray of light when it crosses the boundary between two media. It happens because light has different speeds in different media. A ray of light entering a medium where the speed of light is less (from air to water, for example) bends towards the perpendicular to the boundary of the two media. It bends away from the perpendicular when it crosses from water to air. Refraction was known to ancient Greeks, but Snell, a Dutch mathematician, was the first to study it.

TIMELINE

LIGHT

ROBERT HOOKE (1635-1703)

1670 – England

‘Within the limits of elasticity, the extension ( Strain ) of an elastic material is proportional to the applied stretching force ( Stress )’

Hooke’s law applies to all kinds of materials, from rubber balls to steel springs. The law helps define the limits of elasticity of a material.

In equation form; the law is expressed as F = kx, where F is force, x change in length and k is a constant. The constant is known as Young’s Modulus, after THOMAS YOUNG who in 1802 gave physical meaning to k.

Boyle and Hooke formed the nucleus of scientists at Gresham College in Oxford who were to create the Royal Society in 1662 and Hooke served as its secretary until his death. Newton disliked Hooke’s combative style (Hooke accused Newton of plagiarism, sparking a lifelong feud between the two) and refused to attend Royal Society meetings while Hooke was a secretary.

Hooke mistrusted his contemporaries so much that when he discovered his law he published it as a Latin anagram, ceiiinosssttvu, in his book on elasticity.

Two years later, when he was sure that the law could be proved by experiments on springs, he revealed that the anagram meant Ut tensio sic vis. That is, the power of any spring is in the same proportion with the tension thereof.

At the same time, in 1665 Hooke published his work Micrographia presenting fifty-seven illustrations drawn by him of the wonders seen with the microscope.

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Related sites

• MICROGRAPHIA (www.roberthooke.org.uk)
• National Library of Medicine (archive.nlm.nih.gov)
• HookeMicro (digital.library.wisc.edu)

ANTON VAN LEEUWENHOEK (1632-1723)

1674 – Netherlands

Leeuwenhoek was probably inspired to take up microscopy after seeing a copy of HOOKE’s Micrographia, though as a draper he was likely to have already been using lenses to examine cloth.
Unlike Hooke, Leeuwenhoek did not use a two lens compound microscope, but a single high quality lens, which could be described simply as a magnifying glass rather than a microscope. Leeuwenhoek is known to have made over 500 of these single–lens microscopes. They are simple devices just a few inches long, with the lens mounted in a tiny hole in a brass plate. The specimen is mounted on a point that sticks up in front of the lens. Two screws move the specimen for focusing. All else that is needed is careful lighting and a very steady, sharp eye.

After an introduction to Henry Oldenburg of the Royal Society in London from Dutch physician and anatomist Regnier de Graaf (discoverer of the egg-making follicles in the human ovary which now bear his name), Leeuwenhoek was encouraged to write to the Society’s journal ‘Philosophical Transactions’.

Leeuwenhoek’s letters were translated into Latin and English from the Dutch and he reported seeing tiny creatures in lake-water.

‘ I found floating therein divers earthly particles, and some green streaks, spirally wound serpentwise, and orderly arranged after the manner of copper or tin worms which distillers use to cool their liquors as they distil over. The whole circumference of each of these streaks was about the thickness of a hair of one’s head ’

Leeuwenhoek’s descriptions of ‘animalcules’ in water from different sources – rainwater, pond water, well water, sea water and so on – were verified by independent witnesses, including the vicar of Delft. Hooke too confirmed his findings with his own observations performed in front of expert witnesses, including Sir Christopher Wren.
Leeuwenhoek came close to understanding that bacteria were germs that cause disease but it took another century before LOUIS PASTEUR made that step.

TIMELINE

MICROSCOPY

Related sites

• Micrographia site (www.micrographia.com/)

ISAAC NEWTON (1642-1727)

1687 – England

‘Any two bodies attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them’

NEWTON

The force is known as gravitation
Expressed as an equation:

F = GmM/r²

where F is Force, m and M the masses of two bodies, r the distance between them and G the gravitational constant
This follows from KEPLER’s laws, Newton’s laws of motion and the laws of conic sections. Gravitation is the same thing as gravity. The word gravity is particularly used for the attraction of the Earth for other objects.

Gravitation
Newton stated that the law of gravitation is universal; it applies to all bodies in the universe. All historical speculation of different mechanical principles for the earth from the rest of the cosmos were cast aside in favour of a single system. He demonstrated that the planets were attracted toward the Sun by a force varying as the inverse square of the distance and generalized that all heavenly bodies mutually attract one another. Simple mathematical laws could explain a huge range of seemingly disconnected physical facts, providing science with the straightforward explanations it had been seeking since the time of the ancients. That the constant of gravitation is in fact constant was proved by careful experiment, that the focus of a body’s centre of gravity appears to be a point at the centre of the object was proved by his calculus.

Calculus
The angle of curve, by definition, is constantly changing, so it is difficult to calculate at any particular point. Similarly, it is difficult to calculate the area under a curve. Using ARCHIMEDES’ method of employing polygons and rectangles to work out the areas of circles and curves, and to show how the tangent or slope of any point of a curve can be analyzed, Newton developed his work on the revolutionary mathematical and scientific ideas of RENE DESCARTES, which were just beginning to filter into England, to create the mathematics of calculus. Calculus studies how fast things change.
The idea of fluxions has become known as differentiation, a means of determining the slope of a line, and integration, of finding the area beneath a curve.

Newton’s ideas on universal gravitation did not emerge until he began a controversial correspondence with ROBERT HOOKE in around 1680. Hooke claimed that he had solved the problem of planetary motion with an inverse square law that governed the way that planets moved. Hooke was right about the inverse square law, but he had no idea how it worked or how to prove it, he lacked the genius that permitted Newton to combine Kepler’s laws of planetary motion with the assumption that an object falling towards Earth was the same kind of motion as the Earth’s falling toward the Sun.
It was not until EDMUND HALLEY challenged Newton in 1684 to show how planets could have the elliptical orbits described by Johannes Kepler, supposing the force of attraction by the Sun to be the reciprocal of their distance from it – and Newton replied that he already knew – that he fully articulated his laws of gravitation.

It amounts to deriving Kepler’s first law by starting with the inverse square hypothesis of gravitation. Here the Sun attracts each of the planets with a force that is inversely proportional to the square of the distance of the planet from the Sun. From Kepler’s second law, the force acting on the planets is centripetal. Newton says this is the same as gravitation.

In the previous half century, Kepler had shown that planets have elliptical orbits and GALILEO had shown that things accelerate at an even pace as they fall towards the ground. Newton realized that his ideas about gravity and the laws of motion, which he had only applied to the Earth, might apply to all physical objects, and work for the heavens too. Any object that has mass will be pulled towards any other object. The larger the mass, the greater the pull. Things were not simply falling but being pulled by an invisible force. Just as this force (of gravity) pulls things towards the Earth, it also keeps the Moon in its orbit round the Earth and the planets moving around the Sun. With mathematical proofs he showed that this force is the same everywhere and that the pull between two things depends on their mass and the square of the distance between them.

Title page of Philosophiae Naturalis Principia Mathematica

Newton published his law of gravitation in his magnum opus Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) in 1687. In it Newton analyzed the motion of orbiting bodies, projectiles, pendulums and free fall near the Earth.

The first book of Principia states the laws of motion and deals with the general principles of mechanics. The second book is concerned mainly with the motion of fluids. The third book is considered the most spectacular and explains gravitation.

Why do two objects attract each other?
‘I frame no hypotheses’, said Newton

It was Newton’s acceptance of the possibility that there are mysterious forces in the world, his passions for alchemy and the study of the influence of the Divine that led him to the idea of an invisible gravitational force – something that the more rationally minded Galileo had not been able to accept.
Newton’s use of mathematical expression of physical occurrences underlined the standard for modern physics and his laws underpin our basic understanding of how things work on an everyday scale. The universality of the law of gravitation was challenged in 1915 when EINSTEIN published the theory of general relativity.

1670-71 Newton composes ‘Methodis Fluxionum‘, his main work on calculus, which is not published until 1736. His secrecy meant that in the intervening period, the German mathematician LEIBNIZ could publish his own independently discovered version – he gave it the name calculus, which stuck.

LAWS OF MOTION

1687 – England

• First Law: An object at rest will remain at rest and an object in motion will remain in motion at that velocity until an external force acts on the object

• Second Law: The sum of all forces (F) that act on an object is equal to the mass (m) of the object multiplied by the acceleration (a), or F = ma

• Third Law: To every action, there is an equal and opposite reaction

The first law

introduces the concept of inertia, the tendency of a body to resist change in its velocity. The law is completely general, applying to all objects and any force. The inertia of an object is related to its mass. Things keep moving in a straight line until they are acted on by a force. The Moon tries to move in a straight line, but gravity pulls it into an orbit.
Weight is not the same as mass.

The second law

explains the relationship between mass and acceleration, stating that a force can change the motion of an object according to the product of its mass and its acceleration. That is, the rate and direction of any change depends entirely on the strength of the force that causes it and how heavy the object is. If the Moon were closer to the Earth, the pull of gravity between them would be so strong that the Moon would be dragged down to crash into the Earth. If it were further away, gravity would be weaker and the Moon would fly off into space.

The third law

shows that forces always exist in pairs. Every action and reaction is equal and opposite, so that when two things crash together they bounce off one another with equal force.

LIGHT

1672 – New Theory about Light and Colours is his first published work and contains his proof that white light is made up of all colours of the spectrum. By using a prism to split daylight into the colours of the rainbow and then using another to recombine them into white light, he showed that white light is made up of all the colours of the spectrum, each of which is bent to a slightly different extent when it passes through a lens – each type of ray producing a different spectral colour.

Newton also had a practical side. In the 1660s his reflecting telescope bypassed the focusing problems caused by chromatic aberration in the refracting telescope of the type used by Galileo. Newton solved the problem by swapping the lenses for curved mirrors so that the light rays did not have to pass through glass but reflected off it.

At around the same time, the Dutch scientist CHRISTIAAN HUYGENS came up with the convincing but wholly contradictory theory that light travels in waves like ripples on a pond. Newton vigorously challenged anyone who tried to contradict his opinion on the theory of light, as Robert Hooke and Leibniz, who shared similar views to Huygens found out. Given Newton’s standing, science abandoned the wave theory for the best part of two hundred years.

1704 – ‘Optiks’ published. In it he articulates his influential (if partly inaccurate) particle or corpuscle theory of light. Newton suggested that a beam of light is a stream of tiny particles or corpuscles, traveling at huge speed. If so, this would explain why light could travel through a vacuüm, where there is nothing to carry it. It also explained, he argued, why light travels in straight lines and casts sharp shadows – and is reflected from mirrors. His particle theory leads to an inverse square law that says that the intensity of light varies as the square of its distance from the source, just as gravity does. Newton was not dogmatic in Optiks, and shows an awareness of problems with the corpuscular theory.

In the mid-eighteenth century an English optician John Dolland realized that the problem of coloured images could largely be overcome by making two element glass lenses, in which a converging lens made from one kind of glass was sandwiched together with a diverging lens made of another type of glass. In such an ‘achromatic’ lens the spreading of white light into component colours by one element was cancelled out by the other.

During Newton’s time as master of the mint, twenty-seven counterfeiters were executed.

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GRAVITY

LIGHT

Related articles

• Top 10 Contributors to Space Exploration (listverse.com)
• Newton’s Laws (quantumredpill.wordpress.com)

CHRISTIAAN HUYGENS (1629- 95)

1690 – Holland

HUYGENS

‘Every point on a wavefront can act as a new source of waves’

A line perpendicular to the wave fronts is called a ray and this ray shows the direction of the wave.

The Huygens construction, published in ‘Traite de la Lumiere‘ (’Treatise on Light’, 1690) gives an explanation for the way light is reflected and refracted.

Huygens said that light consists of a disturbance spreading from its source as spherical pressure waves having wave fronts perpendicular to the direction of their motion and correctly anticipated that in a denser medium light would travel more slowly. This hypothesis was largely ignored at the time as it conflicted with NEWTON‘s theory. Huygens’ view, when re-discovered and championed by THOMAS YOUNG (1773-1829) would eventually become the more commonly accepted version.

He invented a pendulum clock (1656) and also discovered Titan, the first observed moon of Saturn (1665).

Huygens discovered that a simple pendulum does not keep perfect time but completes smaller swings faster than big swings. This is because the weight or ‘bob’ of the pendulum follows a circular path. Huygens’ realisation that a pendulum mimicking a circle’s curve does not maintain a perfectly equal swing and that in order to do this it actually needs to follow a ‘cycloidal’ arc, set him on the path to designing the first successful pendulum clock.

Published ‘Horologium‘ (1658), ‘Horologium Oscillatorium‘ (1673) in which he showed that if the bob’s path were a cycloid (the curved path traced out by a point on the rim of a wheel as it rolls along) instead of a circle, it would be isynchronous (keeping equal time) no matter what the length of the swing. He made the pendulum’s swing cycloidal by suspending a rigid pendulum rod on two chords whose swing either way was limited by two plates called cycloidal checks.

GALILEO had considered the timekeeping possibilities of a swinging pendulum and Huygens successfully tied it with an escapement mechanism.
He explored the mathematics associated with pendulums – which led him, together with HOOKE, to an early prediction of the link between the elliptical orbits of the planets and the inverse square law of gravity. His work was a milestone, playing a key part in the understanding of centrifugal force. It helped to confirm Newton’s laws of motion by showing how an object will travel in a straight line unless pulled into a curved path by some other force.

Huygens was one of the founders of the French Académie des sciences in Paris.

TIMELINE

THE STARS

Related sites

• How Stuff Works – Light (science.howstuffworks.com)

EPICURUS (341 – 270 BCE)

Third Century BCE

EPICURUS

Summarized by the Roman author Lucretius, who wrote ‘On the Nature of the Universe’ in 55 BCE – “The light and heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove”. Accurate for the time, when most people thought that sight was associated with something reaching out from the eye ( EMPEDOCLES ).

Plato wrote of a marriage between the inner light and the outer light.

Euclid worried about the speed with which sight worked. He pointed out that if you close your eyes, then open them again, even the distant stars reappear immediately in your sight, although the influence of sight has had to travel all the way from your eyes to the stars and back again before you could see them.

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