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French chemist Antoine Lavoisier died #OTD in 1794.

He is best known for his development of the law of conservation of mass, which states that mass is neither created nor destroyed in chemical reactions. This principle helped to debunk the phlogiston theory, which was a prevailing theory at the time that suggested substances released a material called "phlogiston" when they burned. He also made significant contributions in understanding respiration as a form of combustion.

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Hand sketch engraving made by madamme Lavoisier in the 18th century featured in "Traité élémentaire de chimie" . Lavoisier performed his classic twelve-day experiment in 1779 which has become famous in history. First, Lavoisier heated pure mercury in a swan-necked retort over a charcoal furnace for twelve days. A red oxide of mercury was formed on the surface of the mercury in the retort. When no more red powder was formed, Lavoisier noticed that about one-fifth of the air had been used up and that the remaining gas did not support life or burning. Lavoisier called this latter gas azote. He removed the red oxide of mercury carefully and heated it in a similar retort. He obtained exactly the same volume of gas as disappeared in the last experiment. He found that the gas caused flames to burn brilliantly, and small animals were active in it as Joseph Priestley had noticed in his experiment. Finally, on mixing the two types of gas, i.e. the gas left in the first experiment, and that given out in the second experiment, he got a mixture similar to air in all respects. In his experiments Lavoisier analysed air into two constituents: the one which supports life and combustion, and is one-fifth by volume of air he called oxygen, the other four-fifths which does not he called azote. This latter gas is now called nitrogen. From the two gases he synthesised something that has the characteristics of air.

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British scientist Rosalind Franklin died #OTD in 1956.

Her most famous contribution to science came from her X-ray diffraction images of DNA, particularly Photo 51, which provided crucial evidence for the double helix structure of DNA. Her photo was shared without her knowledge with J. Watson & F. Crick, who used it as a basis for their model of DNA's structure. Their work overshadowed her contribution, & she was not fully recognized for her role until after her death.

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American mathematician and aerospace engineer Mary Jackson died #OTD in 2005.

In 1951 she started working at the National Advisory Committee for Aeronautics (NACA), where she was a member of its West Area Computing unit and Jackson’s supervisor was Dorothy Vaughan. Despite early promotions, she was denied management-level positions, and in 1979 she left engineering and took a demotion to become manager of the women’s program at NASA.

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American physicist and chemist Katharine Burr Blodgett was born #OTD in 1898.

She was the inventor of a technique for making non-reflecting "invisible" glass, a material used in virtually all camera lenses & many other optical devices. She was also responsible for developing an instrument that can measure film thicknesses to within a few angstroms. She did research on methods of removing ice from airplane wings. She is also credited with the development of a new type of smoke screen.

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British surveyor and geographer George Everest died #OTD in 1866.

Everest was largely responsible for surveying the meridian arc from the southernmost point of India north to Nepal, a distance of about 2,400 kilometres, a task that took from 1806 to 1841 to complete. In 1865, the Royal Geographical Society renamed Peak XV – at the time only recently identified as the world's highest peak – to Mount Everest in his honour. via @wikipedia

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Russian mathematician and geometer Nikolai Lobachevsky was born #OTD in 1792.

He is known primarily for his work on hyperbolic geometry, otherwise known as Lobachevskian geometry, and also for his fundamental study on Dirichlet integrals, known as the Lobachevsky integral formula.

Another of his achievements was developing a method for the approximation of the roots of algebraic equations (Lobachevsky method). via @wikipedia

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Austrian Physicist Lise Meitner was born #OTD in 1878. She was the first to pinpoint the atomic phenomenon now known as the Auger effect, but it was credited to Pierre Auger who independently discovered it months after her. Years later when she made a breakthrough in identifying and understanding nuclear fission, her findings were published only under the name of her collaborator, Otto Hahn, who later also received the Nobel Prize for this discovery. via @IAEA

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Henri Becquerel died #OTD in 1908.

He was the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pierre Curie, received the 1903 Nobel Prize in Physics, for the discovery of spontaneous radioactivity. The SI unit for radioactivity, the becquerel (Bq), is named after him. via @wikipedia

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Photographic plate made by Henri Becquerel showing effects of exposure to radioactivity.

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Erwin Schrödinger was born #OTD in 1887.

He was a Nobel Prize-winning who developed fundamental results in quantum theory. In particular, he is recognized for postulating the Schrödinger equation, an equation that provides a way to calculate the wave function of a system and how it changes dynamically in time.

He wrote many works on various aspects of physics, philosophy and theoretical biology and philosophical aspects of science. via @wikipedia

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Actress Hedy Lamarr (nee Hedwig) and composer George Antheil received US patent for their "Secret Communications System", an early version of frequency hopping using a piano-roll to switch among 88 frequencies to make radio-guided torpedoes harder for enemies to detect or jam. The U.S. Navy rejected the idea, then seized it as "alien property" in 1942 (Lamarr was Austrian) but filed it away with no record of a working device being produced. via @wikipedia

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Louis Pasteur successfully tests his vaccine against rabies on Joseph Meister, a boy who was bitten by a rabid dog #OTD in 1885.

Later, people, including 4 children from the United States, went to Pasteur's laboratory to be inoculated. In 1886, he treated 350 people, of which only 1 developed rabies. The treatment's success laid the foundations for the manufacture of many other vaccines. The 1st of the Pasteur Institutes was also built on the basis of this achievement. via @wikipedia

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