Étienne-Louis Malus | |
|---|---|
 Portrait byLouis-Léopold Boilly, 1810 | |
| Born | 23 July 1775 Paris, France |
| Died | 24 February 1812 (1812-02-25) (aged 36) Paris, France |
| Nationality | French |
| Known for | Malus's law Plane of polarization Polarization of light Malus-Dupin theorem |
| Awards | Rumford Medal(1810) |
| Scientific career | |
| Fields | Physics |
Étienne-Louis Malus (/ˈɛt.i.ɛnˈluː.iməˈluːs/;French:[e.tjɛn.lwima.lys]; 23 July 1775 – 23 February 1812) was a Frenchofficer,engineer,physicist, andmathematician.
Malus was born inParis,France and studied at the military engineering school at Mezires where he was taught byGaspard Monge.[1][2] He participated inNapoleon'sexpedition into Egypt (1798 to 1801).[3] He was also a member of the mathematics section of theInstitut d'Égypte. Malus became a member of theAcadémie des Sciences in 1810. In 1810 theRoyal Society of London awarded him theRumford Medal.[1]
His mathematical work was almost entirely concerned with the study oflight.[3] He studiedgeometric systems calledray systems, closely connected toJulius Plücker'sline geometry. He conducted experiments to verifyChristiaan Huygens's theories of light and rewrote the theory in analytical form. His discovery of thepolarization of light byreflection was published in 1809 and his theory ofdouble refraction of light incrystals, in 1810.[2]
Malus attempted to identify the relationship between the polarising angle of reflection that he had discovered, and therefractive index of the reflecting material. While he deduced the correct relation forwater, he was unable to do so for glasses due to the low quality of materials available to him (the refractive index of most glasses available at that time varied between the surface and the interior of the glass). It was not until 1815 thatSir David Brewster was able to experiment with higher quality glasses and correctly formulate what is known asBrewster's law. This law was later explained theoretically byAugustin Fresnel, as a special case of hisFresnel equations.
Malus is probably best remembered forMalus's law, giving the resultant intensity, when a polariser is placed in the path of an incident beam. A follower ofLaplace, both his statement of the Malus's law and his earlier works on polarisation andbirefringence were formulated using thecorpuscular theory of light.[4]
His name is one of the72 names inscribed on the Eiffel tower.[5]
In 1810, Malus, while engaged on the theory of double refraction, casually examined through a doubly refracting prism of quartz the sunlight reflected from the windows of theLuxembourg palace. He was surprised to find that the two rays alternately disappeared as the prism was rotated through successive right angles, in other words, that the reflected light had acquired properties exactly corresponding to those of the rays transmitted through Iceland spar.
He named this phenomenon polarization, and thought it could not be explained by wave theory of light. Instead, he explained it by stating that light-corpuscules have polarity (like magnetic poles).[6]
Malus mathematically analyzed the properties of a system of continuous light rays in three dimensions. He found the equation of caustic surfaces and theMalus theorem: Rays of light that are emitted from a point source, after which they have been reflected on a surface, are all normal to a common surface, but after the second refraction they no longer have this property. If the perpendicular surface is identified with a wave front, it is obvious that this result is false, which Malus did not realize because he adhered to Newton's theory of light emission. Malus's theorem was not proved until 1824 by W. R. Hamilton,[7][8] withAdolphe Quetelet andJoseph Diez Gergonne giving a separate proof in 1825.[9]
