* 1629 – Christiaan Huygens, Dutch mathematician ( d. 1695 )

Diffraction arises because of the way in which waves propagate ; this is described by the Huygens – Fresnel principle and the principle of superposition of waves.

The Huygens – Fresnel principle is one such model ; it states that each point on a wavefront generates a secondary spherical wavelet, and that the disturbance at any subsequent point can be found by summing the contributions of the individual wavelets at that point.

* Christiaan Huygens 1629 – 1695 ( Netherlands )

The Huygens – Fresnel principle ( named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel ) is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction.

The arbitrary assumptions made by Fresnel to arrive at the Huygens – Fresnel equation emerge automatically from the mathematics in this derivation.

The various assumptions made by Fresnel emerge automatically in Kirchhoff's diffraction formula, to which the Huygens – Fresnel principle can be considered to be an approximation.

ro: Principiul Huygens – Fresnel

* Ion and Neutral Camera ( INCA ), an instrument aboard the Cassini – Huygens spacecraft

* 2005 – Landing of the Huygens probe on Saturn's moon Titan.

Among the Laboratory's current major active projects are the Mars Science Laboratory mission ( which includes the Curiosity rover ), the Cassini – Huygens mission orbiting Saturn, the Mars Exploration Rovers ( Spirit and Opportunity ), the Mars Reconnaissance Orbiter, the Dawn mission to the dwarf planet Ceres and asteroid Vesta, the Juno spacecraft en route to Jupiter, the Gravity Recovery and Interior Laboratory ( GRAIL ) mission to the Moon, the Nuclear Spectroscopic Telescope Array ( NuSTAR ) X-ray telescope, and the Spitzer Space Telescope.

* Cassini – Huygens

* 1655 – Saturn's largest moon, Titan, is discovered by Christiaan Huygens.

A second-generation Mariner spacecraft, called the Mariner Mark II series, eventually evolved into the Cassini – Huygens probe, now in orbit around Saturn.

The Huygens – Fresnel equation is one such model.

Examples of the application of Huygens – Fresnel principle can be found in the sections on diffraction and Fraunhofer diffraction.

File: Christiaan Huygens-painting. jpeg | Christiaan Huygens ( 1629-1695 ): studied the rings of Saturn and discovered its moon Titan, invented the pendulum clock, studied optics and centrifugal force, theorized that light consists of waves ( Huygens – Fresnel principle ) which became instrumental in the understanding of wave-particle duality.

* Huygens – Fresnel principle

In the Axioms Scholium of his Principia Newton said its axiomatic three laws of motion were already accepted by mathematicians such as Huygens ( 1629 – 1695 ), Wallace, Wren and others, and also in memos in his draft preparations of the second edition of the Principia he attributed its first law of motion and its law of gravity to a range of historical figures.

The resulting Huygens – Fresnel principle was extremely successful at reproducing light's behavior and, subsequently supported by Thomas Young's discovery of double-slit interference, was the beginning of the end for the particle light camp.

The Cassini – Huygens mission to Titan discovered clouds formed from methane or ethane which deposit rain composed of liquid methane and other organic compounds.

** NASA launches the Cassini – Huygens probe to Saturn.

Augustin-Jean Fresnel did more definitive studies and calculations of diffraction, made public in 1815 and 1818, and thereby gave great support to the wave theory of light that had been advanced by Christiaan Huygens and reinvigorated by Young, against Newton's particle theory.

Wave diffraction in the manner of Huygens and Fresnel

In 1816, Fresnel showed that Huygens ' principle, together with his own principle of interference could explain both the rectilinear propagation of light and also diffraction effects.

Around the same time, Newton's contemporaries Robert Hooke and Christian Huygens — and later Augustin-Jean Fresnel — mathematically refined the wave viewpoint, showing that if light traveled at different speeds in different media ( such as water and air ), refraction could be easily explained as the medium-dependent propagation of light waves.

In the early 19th century, the double-slit experiments by Young and Fresnel provided evidence for Huygens ' wave theories.

According to the Huygens – Fresnel principle, each point on the wavefront of a propagating wave can be considered to act as a point source, and the wavefront at any subsequent point can be found by adding together the contributions from each of these individual point sources.

Huygens achieved note for his argument that light consists of waves, now known as the Huygens – Fresnel principle, which two centuries later became instrumental in the understanding of wave-particle duality.

Huygens ' principle when applied to an aperture simply says that the far-field diffraction pattern is the spatial Fourier transform of the aperture shape, and this is a direct by-product of using the parallel-rays approximation, which is identical to doing a plane wave decomposition of the aperture plane fields ( see Fourier optics ).

However, this article provides an interesting discussion of the limitations of the principle and also of different scientists ' views as to whether it is an accurate representation of reality or whether " Huygens ' principle actually does give the right answer but for the wrong reasons ".

Using Huygens ' theory and the principle of superposition of waves, the complex amplitude at a further point P is found by summing the contributions from each point on the sphere of radius r < sub > 0 </ sub >.

Huygens ' principle can be seen as a consequence of the isotropy of space-all directions in space are equal.

This phenomenon is called Huygens ' principle.

It follows mathematically from Huygens ' principle ( at the limit of small wavelength ), and can be used to derive Snell's law of refraction and the law of reflection.

Classically, Fermat's principle can be considered as a mathematical consequence of Huygens ' principle.

Indeed Fermat's principle does not hold standing alone, we now know it can be derived from earlier principles such as Huygens ' principle.

However, given the above simplifications, Huygens ' principle provides a quick method to predict the propagation of a wavefront through, for example, a spherical wavefront will remain spherical as the energy of the wave is carried away equally in all directions.

The land was near the property of a good friend of Huygens, Count Johan Maurits of Nassau-Siegen, who built his house, the Mauritshuis, around the same time.

Christiaan Huygens, in a letter dated June 8, 1694, wrote to Leibniz, " I do not know if you are acquainted with the accident which has happened to the good Mr Newton, namely, that he has had an attack of phrenitis, which lasted eighteen months, and of which they say his friends have cured him by means of remedies, and keeping him shut up.

It was notable for containing the principles of the stereographic and the orthographic projections, and it inspired the works of Desargues and Christiaan Huygens.

Many leading scientists including Newton and Huygens doubted that such a clock could ever be built and had more optimism for astronomical observations ( such as the Method of Lunar Distances ).

In 1690, Christian Huygens proposed a wave theory for light based on suggestions that had been made by Robert Hooke in 1664.

From its invention in 1656 by Christiaan Huygens until the 1930s, the pendulum clock was the world's most precise timekeeper, accounting for its widespread use.

Optics, for instance, was revolutionized by people like Robert Hooke, Christiaan Huygens, René Descartes and, once again, Isaac Newton, who developed mathematical theories of light as either waves ( Huygens ) or particles ( Newton ).

But Bullialdus did not accept Kepler ’ s second and third laws, nor did he appreciate Christiaan Huygens ’ s solution for circular motion ( motion in a straight line pulled aside by the central force ).

The 17th-century Dutch mathematician Christiaan Huygens discovered and proved these properties of the cycloid while searching for more accurate pendulum clock designs to be used in navigation.

In 1659 Huygens derived the now well-known formula for the centripetal force, exerted by an object describing a circular motion, for instance on the string to which it is attached, in modern notation:

Furthermore, Huygens concluded that Descartes's laws for the elastic collision of two bodies must be wrong, and he formulated the correct laws.

Huygens is remembered especially for his wave theory of light, which he first communicated in 1678 to France's Royal Académie des sciences and which he published in 1690 in his Treatise on light ( see also Huygens-Fresnel principle ).

Huygens was the first to derive the formula for the period of an ideal mathematical pendulum ( with massless rod or cord and length much longer than it's swing ), in modern notation:

Huygens developed a balance spring watch more or less contemporaneously with, though separately from, Robert Hooke, and controversy over who should be given credit for this important invention persisted for centuries.

Huygens ' explanation for the aspects of Saturn, Systema Saturnium, 1659.

Based on this fact, many writers in the past and even the present have given Huygens the credit for inventing the modern form of spiral balance spring in 1675 rather than Hooke's earlier straight spring of 1665 because they considered that the spiral form automatically conferred the property of isochronism on the oscillating balance.

The watches which were made in Paris from C. 1675 and following Huygens plan, are notable for lacking a fusee for equalizing the mainspring torque, showing that Huygens thought that his spiral spring would isochronise the balance, in the same way that he thought that the cycloidally shaped suspension curbs on his clocks would isochronise the pendulum.