On This Day
1818 – French physicist Augustin Fresnel submits his prizewinning “Memoir on the Diffraction of Light”, precisely accounting for the limited extent to which light spreads into shadows, and thereby demolishing the oldest objection to the wave theory of light.
Augustin-Jean Fresnel (/ˈfreɪn-, ˈfrɛn.ɛl, -əl/ FRAYN-, FREN-el, -əl or /freɪˈnɛl/ fray-NEL; French: [oɡystɛ̃ʒɑ̃ fʁɛnɛl]; 10 May 1788 – 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Newton’s corpuscular theory, from the late 1830s  until the end of the 19th century. He is perhaps better known for inventing the catadioptric (reflective/refractive) Fresnel lens and for pioneering the use of “stepped” lenses to extend the visibility of lighthouses, saving countless lives at sea. The simpler dioptric (purely refractive) stepped lens, first proposed by Count Buffon  and independently reinvented by Fresnel, is used in screen magnifiers and in condenser lenses for overhead projectors.
By expressing Huygens’ principle of secondary waves and Young’s principle of interference in quantitative terms, and supposing that simple colors consist of sinusoidal waves, Fresnel gave the first satisfactory explanation of diffraction by straight edges, including the first satisfactory wave-based explanation of rectilinear propagation. Part of his argument was a proof that the addition of sinusoidal functions of the same frequency but different phases is analogous to the addition of forces with different directions. By further supposing that light waves are purely transverse, Fresnel explained the nature of polarization, the mechanism of chromatic polarization, and the transmission and reflection coefficients at the interface between two transparent isotropic media. Then, by generalizing the direction-speed-polarization relation for calcite, he accounted for the directions and polarizations of the refracted rays in doubly-refractive crystals of the biaxial class (those for which Huygens’ secondary wavefronts are not axisymmetric). The period between the first publication of his pure-transverse-wave hypothesis and the submission of his first correct solution to the biaxial problem was less than a year.
Later, he coined the terms linear polarization, circular polarization, and elliptical polarization, explained how optical rotation could be understood as a difference in propagation speeds for the two directions of circular polarization, and (by allowing the reflection coefficient to be complex) accounted for the change in polarization due to total internal reflection, as exploited in the Fresnel rhomb. Defenders of the established corpuscular theory could not match his quantitative explanations of so many phenomena on so few assumptions.
Fresnel had a lifelong battle with tuberculosis, to which he succumbed at the age of 39. Although he did not become a public celebrity in his lifetime, he lived just long enough to receive due recognition from his peers, including (on his deathbed) the Rumford Medal of the Royal Society of London, and his name is ubiquitous in the modern terminology of optics and waves. After the wave theory of light was subsumed by Maxwell’s electromagnetic theory in the 1860s, some attention was diverted from the magnitude of Fresnel’s contribution. In the period between Fresnel’s unification of physical optics and Maxwell’s wider unification, a contemporary authority, Humphrey Lloyd, described Fresnel’s transverse-wave theory as “the noblest fabric which has ever adorned the domain of physical science, Newton’s system of the universe alone excepted.” 
Born On This Day
1896 – Maria L. de Hernández, Mexican-American rights activist (d. 1986)
María Rebecca Latigo de Hernández (July 29, 1896 – January 8, 1986) was a Mexican-American rights activist. She was born in San Pedro Garza García, Mexico. During the 1930s, she spoke publicly and demonstrated on behalf of Mexican Americans about their education in the United States. She and her husband, Pedro Hernandez Barrera, founded Orden Caballeros de America on January 10, 1929. She organized the Asociación Protectora de Madres in 1933. In 1970 she was active in the Raza Unida Party.
María Rebecca Latigo de Hernández was born in 1896 in Garza García near Monterrey, Nuevo León, Mexico. Her father was a professor. As a young adult, she taught at an elementary school whilst she lived in Monterrey, Mexico.
The Hernández family owned and ran a grocery store and bakery. She fought and wrote against the segregation, racial oppression, and poor education that the Mexican American children were receiving.
In 1929, the Hernández family helped to organize and found the Order of the Knights of America, or the Orden Caballeros de America. The Order of Knights of America was a committee dedicated to political and civil activists in order to help Mexican Americans as well as Mexican immigrants. They helped with matters including educational and social, but the organization was largely focused on educational matters. The main audience targeted by their organization was Mexican American business owners. However, they also set a goal to help both male and female school aged children.
In 1932 María Rebecca Latigo de Hernández was the first Mexican female announcer on the radio. In 1933 she helped open an association to help expecting mothers, which was known as Asociación Protectora de Madres.
In 1934 María, along with her husband and children, helped to manage an organization which helped to create safe places, and better the education for the West Side Mexican Communities. It was named La Liga de Defensa Pro-Escolar. In connection to her radio career, she spoke to promote Council 16 of the League of United Latin American Citizens on a program called the “Voz de las Americas”. The league became well managed in December 1934. She supported the efforts of the league in 1940,and then again in 1947. During the years with the league, she helped to encourage equality for all Mexican Americans, no matter where they were from or where they were living.
In 1938 she began working with the pecan-shellers’ strike, with a cause for women workers’ rights. The strike had begun as a way for women to obtain safer working conditions as well as increased salaries. In 1939 she was included in a group of women, who were able to visit then Mexican President, Lázaro Cárdenas. The women went to communicate the goodwill between Mexicans from Mexico and Mexican Americans in the United States.
In 1945 “México y Los Cuatro Poderes Que Dirigen al Pueblo” (En: Mexico and the Four Powers that Lead the People) was published. In this essay, she said that domestic sphere founded society. It also stated that mothers were the creators of nations. Close to the time that her essay was published, she was also involved in organizing Club Liberal Pro-Cultura de la Mujer.
In 1968 she was a regular guest on San Antonio television, informing the public about education and social progress. In 1969, María Rebecca Latigo de Hernández was appointed the position of Treasurer of the order’s board of directors, as well as the President of Circulo Social. In 1970 she grew her political activities by joining the Raza Unida Party. She served as a key-note speaker at the Raza Unida’s Statewide Conference, located in Austin, Texas.
Hernández was married in 1915 at the age of 19 to Pedro Hernández Barrera. They were married in Hebbronville, Texas. They moved to San Antonio, in 1918, where they settled down, and their family eventually grew to include 10 children.
She died of pneumonia on January 8, 1986. She is buried in the plot of the Orden Caballeros de América outside of Elmendorf, Texas.
She was featured as the subject of Google Doodle on July 29, 2018.
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