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Carl Friedrich Christian Mohs (/ m oʊ z / MOHZ, German: [ˈfʁiːdʁɪç ˈmoːs]; 29 January 1773 – 29 September 1839) was a German chemist and mineralogist. He was the creator of the Mohs scale of mineral hardness. [1] Mohs also introduced a classification of the crystal forms in crystal systems independently of Christian Samuel Weiss. [2]
Quartz clocks and quartz watches are timepieces that use an electronic oscillator regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency , so that quartz clocks and watches are at least an order of magnitude more accurate than mechanical clocks .
Friedrich Mohs (lithograph by Joseph Kriehuber, 1832) Felix Karl Ludwig Machatschki (1895–1970) George Mackenzie (1780–1848) Ernest-François Mallard (1833–1894) Joseph A. Mandarino (1929–2007) Ho-Kwang Mao (born 1941) Brian Harold Mason (1917–2009) Johannes Mathesius (1504–1565) Charles-Victor Mauguin (1878–1958) John Mawe (1764 ...
1923 - William H. Bragg and Reginald E. Gibbs elucidated the structure of quartz. [70] [71] 1923 - Paul Peter Ewald published his book Kristalle und Röntgenstrahlen (Crystals and X-rays). [72] 1924 - Louis de Broglie in his PhD thesis Recherches sur la théorie des quanta [73] introduced his theory of electron waves. This was the start of ...
For example, some sources have assigned a Mohs hardness of 6 or 7 to granite but it is a rock made of several minerals, each with its own Mohs hardness (e.g. topaz-rich granite contains: topaz — Mohs 8, quartz — Mohs 7, orthoclase — Mohs 6, plagioclase — Mohs 6–6.5, mica — Mohs 2–4).
Auguste-Lucien Vérité (1806–1887), French clockmaker, Beauvais, astronomical clock. Friedrich Adolph Nobert (1806–1881), German mechanic and optician, Barth. Johann Carl Rahsskopff (1806–1886), German clockmaker and mechanic, Koblenz, clocks with worm gears.
The first clock known to strike regularly on the hour, a clock with a verge and foliot mechanism, is recorded in Milan in 1336. [96] By 1341, clocks driven by weights were familiar enough to be able to be adapted for grain mills, [97] and by 1344 the clock in London's Old St Paul's Cathedral had been replaced by one with an escapement. [98]
[3] [4] The Mohs scale is based on relative scratch hardness of different materials; with talc assigned a value of 1 and diamond assigned a value of 10. [5] Mohs's scale had two limitations: it was not linear, and most modern abrasives fall between 9 and 10.; [6] [7] so, later scientists attempted to increase resolution at the harder end of the ...
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