Huygens, Christian

Huygens Christian (1629-1695) invented pendulum, conservation mobility (= mv) Jesenak Viktor (1926-2000) Slovak chem., expert in solid-state kinetics Jorgensen Sven Erik( 9A2-), Danish phys., inventor of thermodynamics for ecological systems... 

Huygens, Christian (1690). Trade de la lumiere, published in Leyden. (English translation Treatise on Light by S. P. Thompson, London Macmillan Co.,... 

The faces and angles of natural crystals result from the orderly arrangements of the atoms and molecules that make up a crystal. The relation between crystal shape and microscopic structure was suggested in the seventeenth century by Robert Hooke and Christian Huygens. It was confirmed in the twentieth century with the development of x-ray diffraction, a technique that uses x rays to examine the atomic structures of materials. 

The third stage in the development of the modern thermometer began in 1665 with the development of the first thermometric standard scale. In that year Robert Boyle, Robert Hooke, and Christian Huygens suggested independently that thermometers could be calibrated effectively from a single fixed point. Degrees would represent a standard expansion or contraction fraction of the volume of the thermometric substance measured at the fixed point. Boyle set the fixed point at the freezing tempera-... 

H—Hardness. There are different types of hardness. Why Because the value of a material s hardness depends on how it is tested. The hardness of a material is its resistance to the formation of a permanent surface impression by an indenter. You will also see it defined as resistance of a material to deformation, scratching, and erosion. So the geometry of the indenter tip and the crystal orientation (and therefore the microstructure) will affect the hardness. In ceramics, there tends to be wide variations in hardness because it involves plastic deformation and cracking. Table 16.4 lists hardness values on the Mohs hardness scale, a scratch test that can be used to compare hardness of different minerals. For example, quartz has a Mohs hardness of 7, which made flint (a cryptocrystalline quartz) particularly useful in prehistoric times for shaping bone (the mineral component is apatite with hardness 5) and shell (the mineral component is calcite with hardness 3). Mohs hardness scale was not the first scratch hardness technique. As long ago as 1690, Christian Huygens, the famous astronomer, had noticed anisotropy in scratch hardness. 

Andriesse, Cornells D. Christian Huygens. Paris Albin Michel, 2000. 

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