Paul Peter Ewald (January 23, 1888 - August 22, 1985) was a U.S. (German-born) crystallographer and physicist. He was a pioneer of the X-ray diffraction methods. He was also the eponym of Ewald construction and the Ewald sphere. He was the father-in-law of Hans Bethe. January 23 is the 23rd day of the year in the Gregorian Calendar. ... 1888 is a leap year starting on Sunday (click on link for calendar). ... August 22 is the 234th day of the year in the Gregorian Calendar (235th in leap years), with 131 days remaining. ... 1985 is a common year starting on Tuesday of the Gregorian calendar. ... The United States of America — also referred to as the United States, the U.S.A., the U.S., America, the States, or (archaically) Columbia—is a federal republic of 50 states located primarily in central North America (with the exception of two states: Alaska and Hawaii). ... The word physicist should not be confused with physician, which means medical doctor. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... An eponym is a person (real or fictitious) whose name has become identified with a particular object or activity. ... In solid state physics, in particular crystallography, the Ewald construction is a method for reconstructing a crystal structure by examining and interpreting an x-ray diffraction pattern. ... Ewalds sphere is a geometric construct used in X-ray crystallography which neatly demonstrates the relationship between (a) the wavelength of the incident beams of light, (b) the angle of diffraction for a given reflection, (c) the unit cell and reciprocal unit cell of the crystal, and (d) the... Hans Albrecht Bethe (born July 2, 1906), is a German-American physicist from Strassburg (then part of Germany, now Strasbourg, France). ...

Paul Peter Ewald was awarded the Max Planck medal in 1987. The Max Planck medal is an award for extraordinary achievements in Theoretical Physics. ... 1987 is a common year starting on Thursday of the Gregorian calendar. ...

Ewald wrote several books on the mechanics of solids and liquids, one of which, The Physics of Solids and Fluids (London, Blackie and Son, 1930) was in collaboration with the physicists Th. Pöschl and Ludwig Prandtl. (Also see Prandtl number, an important dimensionless measure of the ratio of the diffusion of momentum and of heat in fluid dynamics.) Prandtl Number is a dimensionless number approximating the ratio of momentum diffusivity and thermal diffusivity, It is defined as: where is the kinematic viscosity and α is the thermal diffusivity. ...