Guillaume Amontons

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Guillaume Amontons
Guillaume Amontons.png
Guillaume Amontons, Luxembourg Garden, 1690
Born31 August 1663
Paris, France
Died11 October 1705 (1705-10-12) (aged 42)
Paris, France
Known forTribology
Scientific career

Guillaume Amontons (31 August 1663 – 11 October 1705) was a French scientific instrument inventor and physicist. He was one of the pioneers in studying the problem of friction, that is the resistance to motion where bodies are in contact.


Guillaume was born in Paris, France. His father was a lawyer from Normandy who had moved to the French capital. While still young, Guillaume lost his hearing, which may have motivated him to focus entirely on science. He never attended a university, but was able to study mathematics, the physical sciences, and celestial mechanics. He also spent time studying the skills of drawing, surveying, and architecture. He died in Paris, France.


He was supported in his research career by the government, and was employed in various public works projects.

Scientific instruments[edit]

Among his contributions to scientific instrumentation were improvements to the barometer (1695), hygrometer (1687), and thermometer (1695), particularly for use of these instruments at sea. He also demonstrated an optical telegraph and proposed the use of his clepsydra[1] (water clock) for keeping time on a ship at sea.


Amontons investigated the relationship between pressure and temperature in gases though he lacked accurate and precise thermometers. Though his results were at best semi-quantitative, he established that the pressure of a gas increases by roughly one-third between the temperatures of cold and the boiling point of water.[2] This was a substantial step towards the subsequent gas laws and, in particular, Gay-Lussac's law. His work led him to speculate that a sufficient reduction in temperature would lead to the disappearance of pressure. Though he came close to finding absolute zero - the theoretical temperature by which the volume of air in his air-thermometer will by reduced to nothing (estimated by him as −240 on the Celsius scale),[3] the discovery would not be complete until at least a century later.

Guillaume Amontons is also the inventor of the hot air engine[4]. In 1699 he built his first engine, means over one century before the well-known Stirling Engine[5]. This engine, named by Amontons "FIre Mill" was following a new thermodynamic cycle, that later became the Stirling cycle.

The fire mill is a wheel that make use of the heated air and its expansion to generate motive power. The calculated power of Amontons' Fire Mill was 39 HP ; this was the level of power of the most powerful hot air engines of the 19th century (excepted the Caloric Engine of Ericsson[6]). The main difference between the Amontons engine and the future hot air engines was the nature of the piston (Amontons used water) and the use of rotationnal motion instead of the alternating motion.


Free-body diagram for a block on a ramp. Arrows are vectors indicating directions and magnitudes of forces. N is the normal force, mg is the force of gravity, and Ff is the force of friction.

In 1699, Amontons published his rediscovery of the laws of friction first put forward by Leonardo da Vinci.[7] Though they were received with some scepticism, the laws were verified by Charles-Augustin de Coulomb in 1781.[8]

Amontons' laws of friction[edit]

Amontons' laws of friction:[9]

  1. The force of friction is directly proportional to the applied load. (Amontons' 1st law)
  2. The force of friction is independent of the apparent area of contact. (Amontons' 2nd law)
  3. Kinetic friction is independent of the sliding velocity. (Coulomb's law)

(These 3 laws only apply to dry friction, in which the addition of a lubricant modifies the tribological properties significantly.)

The laws are shown by the classic example of a brick resting on an inclined plane, where it is in equilibrium and thus motionless. The force of gravity is opposed by static friction and as the angle of tilt of the plane is increased, the brick will eventually start to move downwards as gravity overcomes the frictional resistance.


See also[edit]


  1. ^ Amontons, G. (1695), Remarques et expériences physiques sur la construction d'une nouvelle clepsydre, Paris.
  2. ^ Amontons (20 June 1699) Moyen de substituer commodement l'action du feu, a la force des hommes et des cheveaux pour mouvoir les machines (Method of substituting the force of fire for horse and man power to move machines), Mémoires de l'Académie royale des sciences, in: Histoire de l'Académie royale des sciences, pp. 112-126.
  3. ^ Wikisource Chisholm, Hugh, ed. (1911). "Cold". Encyclopædia Britannica (11th ed.). Cambridge University Press.
  4. ^ "Amontons' engine".
  5. ^ "Stirling's 1816 engine".
  6. ^ "Ericsson Caloric Engine".
  7. ^ Amontons (19 December 1699) De la resistance causée dans les Machines, tant par les frottemens des parties qui les composent, que par roideur des cordes qu'on y employe, & la maniere de calculer l'un & l'autre (On the resistance caused in machines, both by the rubbing of the parts that compose them and by the stiffness of the cords that one uses in them, & the way of calculating both), Mémoires de l'Académie royale des sciences, in: Histoire de l'Académie royale des sciences, pp. 206-222.
  8. ^ Bowden, F.P. & Tabor, D. (1950) The Friction and Lubrication of Solids pp1, 87-89
  9. ^, Introduction to Tribology - Friction

Further reading[edit]

  • Asimov's Biographical Encyclopedia of Science and Technology, Isaac Asimov, Doubleday & Co., Inc., 1972, ISBN 0-385-17771-2.
  • Cardwell, D.S.L. (1971). From Watt to Clausius: The Rise of Thermodynamics in the Early Industrial Age. Heinemann. ISBN 0-435-54150-1., pp18-19

External links[edit]